I have a 90 740 sedan, had it almost 6 years. It's been great, has 260,000. So I'm not in the dark about these cars.
I got the 91 wagon from a friend. I have all service records which have been far more extensive than mine, but with 100,000 Less miles.
I posted about shocks, now want to put all other questions in one post.

1. shifter moves when braking, and there's a sense of things moving about underneath. I looked at the two front motor mounts and can't see anything obviously wrong, they are the oil filled. Can I think that the trans mount may be the biggest issue here? I couldn't get far enough under the car to see.

2.Air cond. Car was converted to R134 by a very knowledgeable mech 2 years ago. I haven't been able to contact him yet to ask about this.
When I got the car she said the air used to work great but lately it's erratic. It blew pretty cold a couple of times the first day or two but now not really at all, a few days later. Top it up? check for leaks I suppose, but anything else? Could a loose-ish belt be the only issue? I haven't been able to access my tools yet to do that, will be able to in a day or two.

3. radio. Will one from a 92 960 be made to fit? I got the vin # so the dealer can/may give me the code. The faceplate is not the same, the one in the car has a bigger face. The 960 is a simple rectangle. Do I get a box/insert that it fits into?

4. antenna. was broken off, got one from an 88. mostly the same, same plug. Didn't have my test light available, but nothing happened when I plugged it in, motor didn't run, the old one didn't either. Comments? of course I'll chase down whether there's power to it.

Thanks for reading, I'm sure it's frustrating without more detail and checking the obvious but my tools aren't where I can get them yet. Shortly though.