Just this month I took a pair of front struts off a 1991 745 (Wagon/5 door) and put them on my 1985 745. They were different but they did fit. The differences I noticed were: the newer struts with the axle and hub were set up for ABS brakes and the axle nut was much larger (It's likely a different bearing per this "brickboard" link:
http://www.brickboard.com/FAQ/700-90...PartHubRebuild). Despite these differences the old brake rotor still fit perfectly. I just left the hole for the ABS sensor empty. The brake caliper attached to the spindle even though the 1991 brakes only had one piston whereas my 1985 has two pistons.
I've driven the car over 1,000 miles since the swap and all seems just fine.
I got both complete struts with spindle and hub for under $100 at my local Pick-n-Pull. I've saved the originals for a rebuild and will put in new struts, dust boots and bump stops once it's necessary.