OK I know what I need to buy to convert a T4 engine to fit in a bug but what about the electrics? I think the 911 alternator is 90amps which is more than the VW one, right? Anything need to be replaced on a 12v bug? Like bulbs, wiper motor, switchs, relays, coil, etc?
You'll be fine as long as you use the regulator to suit the Porsche alternator, it may even be built-in, I don't know. 
Just be careful with the reported overcooling the porsche 11blade fan setup can cause on a fairly mild type IV engine. Unless you are running high
compression which will see high head temps, the 911 fan may provide too much cooling which is supposedly almost as bad as overheating.
See the http://www.shoptalkforums.com Type 4 site and do a search for 911 or
something and you'll come up with heaps of posts. Sorry this has nothing to do with electrics, but maybe that sight might help as well?
If it is a 12v bbug and the alternator is 12v (which I very much assume it would be) then as KK said it will be fine as long as it has a regulator. If it is not built in, then you will need to wire in to the one in the bug, or fit one from something else. It is pretty easy, as there are not many wires involved. An auto elec will be able to do it a cinch for you. Or have a look at any other external reg vehicle, and you will see how easy it can be.
Go to http://www.aircooledtechnology.com
A 911 shroud even with a 5 blade and a small pulley will overcool pretty much any Type 4 under 2.4 L, unless it is running high compression or working
really hard all the time. not to mention also costing a small fortune.
overcooling is worse than overheating sometimes as the engine can't heat up to proper operating temp, clearances stay too large, oil won't
get hot enough to clean all the crap in it etc.
make sure u get a genuine 911 alternator, not a watercooled VW one. The 911 alternator has the proper thrust bearing inside it. Other alternators
are just designed to handle the load of a fanbelt, rather than the thrust of a 911 fan at 5000rpm.
Yeah, I read about over cooling but can't I just have vents in the shroud to vent air out? Is it a silly idea?
u mean vents in the 911 shroud??? wouldn't that just suck air in from there? I know sharpebuilt also makes a t4 into t1 fan shroud which is
based on the standard doghouse one. its more suited to a mild type 4. Forget the 911 shroud unless your engine can make enough heat for it,
overcooling will quickly wear out your engine.
http://www.sharpbuilt.com.au
You would want the pulley ratio to be approx 1:1.3
cheers