If you take the flywheel, be sure to keep the starter too. Early and late units don't match - ring gear and starter are a different pitch.
I'd definitely grab the diff - I have a 3.73 medium case LSD from an '87 325is in mine - great upgrade for highway cruising. Bolts right in. I'd grab the whole rear subframe while I was at it - overhaul one & swap it all out at once. Driveshafts are the same as well.
Lots of other chassis stuff will swap, of course. Cruise control can be made to fit, gauge clusters are the same except for the coding chip. I'm not sure of anything else, to tell you the truth. Maybe the engine accessories? P/S pump & alternator look similar, but I have no firsthand idea if they'd work. Many Bosch alternators use the same internal parts inside different case halves.