I'm considering buying an older '85 745 Turbo thats for sale around a family member, it just needs a new coil and starter.

Can I use parts off any redblock or did they change between the different Bosch systems? (2.2 vs 2.4)

 

Starters are the same, coils, the Reginas are different. (some 1989-1994 740, 940)

 

AC Compressors the same too? I know the '91s got a different, more diy-friendly AC setup.

I intend on mixing up my '91 with this '85, '85s cosmetically in better shape with less miles (140k vs 197k) but my '91 has the bigger brakes, ABS, stuff like that, both are wagons.

 

AC is probably not the same. Other parts, hard to say, brakes are different, FI is different.

 

the 85 turbo will be LH2.2, while the 91 will be LH2.4, so fuel injection parts are largely not interchangable.

swapping in ABS on a non-ABS car is a fairly complex bunch of stuff to move.

85 is in the middle of the biodegradable wiring harness era.