So, I finally got hold of a black-face 1972-on style clock (thanks, Fasty1973). My earlier hopes that this thing would be easily fixable took a dive on finding out that one of the bearings on the winder flywheel was broken loose and wasting about 80% of the solenoid kick, even after I cleaned up the points and freed up the mechanical guts of the thing.
All was not lost, however.

With a lot of mucking around, I worked out how to adapt the quartz movement from a $5 Ikea alarm clock into the VDO face and instrument bucket. For the first time in quite a few decades my car now has a clock that actually does something useful while looking pretty damn factory.

If anybody wants to give it a shot, just reply and I'll post some photos and a how-to some time in the next few weeks when I have time.

That's brilliant mate. I've got a spare that's not working properly so would love to see how you did it.
Terry

I need to do the same to my earlier clock.

Okay - bear with me - haven't posted pics before.
Here's our victim - the five-buck Ikea alarm clock. We want the clock hands and the quartz movement. Six screws and she's out. Transparent clock-face moulding can be levered out with a blade, and the hands are a push-on, pull-off fit to their respective concentric drive wheels. I ditched the alarm-set hand, because who the hell needs that?
In the late model VDO clock, the mechanical movement is completely enclosed by the steel instrument can, so you need to unscrew the nuts at the back and un-stake the can from the steel rim by un-bending the staked tabs at three points around the circumference. Carefully pull it away and there's the black rim pressing, the plastic disc with the clock numbers printed on, and behind that a black steel light diffuser.
Continued......
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So that leaves you with the mechanical clock drive, attached to the black clock face by two black grub screws. The hands can be gently pulled off what I am going to call their stub-axles because I have no idea what the technical term is. Bag the mecho and chuck it in your spares stash to baffle future generations.
The hole in the centre of the clock face needs to be subtly bored out - about 1mm or so - before the Ikea movement will sit happily flush on top of it. When it fits, a small blob of silicone sealant in each of the four corners of the movement will glue it nicely to the back of the clock face.
I wanted to relocate the battery for two reasons. One is that you emphatically do not want to have to crack this assembly apart every couple of years just to change the battery. And two is that shifting the battery gives you a convenient bit of plastic real estate to attach a bracket and a mounting bolt to. So make up a couple of leads with female spade terminals and gently pull the battery contacts free so you can make them into spades and push the terminals on. Heatshrink for insulation. And feel really lucky about how the Ikea clock movemen fits almost perfectly around the diameter of the clock face, like this was always meant to be. Here, hopefully, is a picture....

Stage Three is where you paint the hands white to match all your other instruments and so that they're not damn invisible against the black clock face. Use a slightly off-white for the best match. The Ikea hands are slightly more squared-off than standard. If you were going for showcar gold, you'd clip the original VDO hands and superglue them to the Ikea ones for a totally original look, but my objective was to make this whole conversion potentially reversible in case I retire, go insane and decide to rebuild the mechanical system some day. And mutilating NLA parts is something I can't make myself do.
Anyway, ensure the alarm switch is off (glue it off if you're paranoid), remove the now-useless alarm adjusting knob (it pulls off) and the time adjuster as well. The bad news is, that adjuster's about to spend its life a long way out of your reach inside the instrument can. The good news is, that adjuster shaft fits a BiC biro ink tube spot-on perfect. Bore a hole in the back of the can and you've got an extension you can reach from behind the dashboard. The original adjuster (through the front of the lens) will now be useless with the new hands, but mine was incomplete and busted anyway. If yours is nice, leave it on as decoration. I left mine off. Here's some pictures, and I'll hopefully get some time to post the rest of the job later....

Alrighty - we're up to the part where we have to suspend the quartz movement/clock face unit the right distance away from the back of the instrument can, lined up properly so the lines on the face match up with the numbers on the plastic lens and centred as nicely as possible all the way around. My calipers measured the face at 72mm diameter and the inside of the can at 83mm, so near enough a 5mm offset all round for true centre. See the wood block in one of the photos? That was a test spacer I worked on to get the right spacing between the black steel conical light diffuser and the clock face. Too much space and it'll look gappy and show the white-painted interior of the can. Not enough and you won't get enough of that groovy bluish light shining on the face with your dashboard lighting on. I worked out a standoff of 18-20mm from the inside rear face of the can was pretty right, and made an aluminium bracket to suit.
My plan was to secure the bracket with a couple of machine screws through the back of the can. One of the original holes was usable, but I drilled an extra one almost dead-centre to positively locate it at two points as insurance against any movement. The next photos show how I centralised the clock face within the can by slightly planing four little sticks of dowel to use as guides. The dowels are temporarily sticky-taped to the inside of the can.
When I was happy with the alignment in all dimensions, I marked the positions for the pilot holes in the bracket by shooting a quick hit of black spray paint on the back of the can, through the mounting holes so they marked the spots on the back of the bracket, then drilled and tapped the holes. I added another, bigger hole in the can to allow the biro ink tube extension for the time adjuster to hang out of the back of the whole thing. Obviously before doing all this I've bolted the bracket to the new clock movement, using the redundant space in the battery recess. A couple of photos:

Got this far? Onya. The hard work's done. Little square cutaways at the 9 and 3 positions on the diffuser cone engage with tabs on the plastic outer lens to line those two things out, and another tab at 6 o'clock locates those two on the instrument can. The rim fits over both, and your clock's reassembled. Rather than stake the rim back on (too violent for old plastic parts, I reckon), I sealed the joint up with a bead of silicone.
Previous photos have shown the little single AA battery holder, which I connected via a twin-pin plug to the clock assembly. The battery holder is siliconed unobtrusively out of sight on top of my steering column tube under the dash. Also note the leads are led out of the can through the same slotted hole which used to house the positive pin for the old clock mechanism. Reminder: Tape your old clock power lead so there's no possibility of a short. Connect it all up and there's your dashboard clock, functional again and ready to remind you how late you are for everything.
Improvements? Well, somebody could always come up with a voltage dropper to take the car system down to 1.5V and eliminate the AA altogether. But that'd add to the cost, and anyway, I like the idea that it doesn't run down the car battery (though, given its current requirements it'd take a long time to do that) or need to be reset every time you disconnect the 12V system.
'71 and earlier owners, you're on your own, sorry. The same Ikea movement would be heaps easier to mount on these because it could go straight on the back of your shorter can, but as for adapting the hand drive system, I haven't even looked at what you'd have to deal with. Sort it out and you'd be the champion.

Awesome job Lo-tech.
I'll have to work mine out as it's a European Clock with quite a different back. Still gives me the gist of the plan though.
Thanks for your description.