Yep. I did the same with my 740 Turbo. I bought a nice 940 and stripped it out as well.
Transferred over the complete interior including all the trim, seats etc with the exception of the dash and instruments.
Also moved over all the suspension components and the Girling Big Brakes. Much better system and the roll bars are thicker than the 740's. Got the later AW71 Gearbox moved over and did the accumulator mod on it. Nice crisp changes now.
This shows the 940 leather seats moved into the 740 Turbo. As you said just a small mod to get the rear seat back to fit.


Finished car with the 940 wheels

Have one of each now
Let me know if you hear of a 90+ exhaust manifold anywhere.
Cheers - Fitzy - Gold Coast