24v will go in but you will need to do a few mods to make it all work:
- alter the sump to clear the steering rack
- alter the end of the crank to take a rwd-type flywheel
- new (custom) exhaust manifolds
- alter the inlet plenum to move the air intake towards the front of the engine bay.
- wiring, ecu and sensors?
It can be done and has been done on several GTVs and 75s, but it isn't as straightforward as dropping in a 12v 3.0 from a 75.
For suspension and brake upgrades I would recommend RS Racing (http://www.alfaromeo-performanceparts.com/shop/
). They are not in the UK but do ship here via their online shop. They developed their suspension kits at the Nurburgring and run the '75 Experience' cars there, so it should be up to the job. I've also bought some suspension parts for my 75 from Performatek.com
in the US. They were very helpful and the exchange rate is very good at the moment
Slippy diff gearbox from the 75 will go straight in, but you will need to mod the gear linkage slightly. 3.0 and 2.0 twinspark 75's have an LSD as standard. These two have identical gearboxes apart from the final drive ratio, which is lower on the 2.0. If you are going for a GTA engine, or a revvier tuned 12v engine, then go for the 2.0 twinspark box unless you want to be geared for 180mph!
Hope that gives you a few ideas, and maybe someone with some better knowledge than me will be along to help you further.