Dave is spot on. The number of possible swap Qs is infinite. Ask on the BBRD and someone will know. Re: seats. 740s wont fit a 240, too wide. 240s fit all 240s. Headrests changes with the 1986 year, the support rods are a tad farther apart. The entire seat is swappable, though. BTDT.

Lotsa other parts swap, too. changing things that are involved with engine computers, fuel injection, ignition control, etc, require swapping wiring and computers and sensors.

The 1983 and 1984 year 240s are special. Earlier and later years have differences. 1983-4 have the B23F engine (if not turbo), not like 82 or 85+.
that means the AMM and ICM and ECU are just for those years. No swaps with other years. The B23F engine is a right stout worker. Easy to work on, able to run for-dang-near-ever if cared for. Same for the transmissions.

Good Luck,

Bob

:>)