I've just installed retractable seatbelts in the front of my 72/3 kombi and planned on moving the old (Static) belts to the middle seats.
However they dont seem long enough.
Are they a completely different part ?

You need different belts. The top part is longer and the short bit is longer.

For my bus i wanted adjustable ones cause at the moment they bolt to the seat - i want to bolt then to the floor. The set of belts would have costed $250 approx - but luckily a mate wanted a new middle seat for his bus.
He bought an early Tarago middle seat and got a perfect set of belts exactly like i wanted. He was happy with the money he paid for the seat so i donated i box of amber!

The 'retractables' in the front of our 76 camper dont retract anymore can you fix this yourself or do you need to buy newies?

Probably not a good idea to try to fix the seat belt reel. You can buy brand new rectracting seat belt kits at Repco. They come in a variety of sizes and lengths, but all include new reels, belts, buckles, latches on stalks, brackets and all mounting bolts. They're about $55 a side.

My Campmobile was missing the right-hand belt on the rear (which is a lap-belt only). After a long search through a large wrecking yard I found that Austin Tasmans have the same purple belt and latch design as my Kombi. I was told they are Kingswood belts but they aren't.