Having busted my chops to put a 5.0 in a straight six car, I have the following observations:
It is best done with the straight six crossmember, and a Fairmont unit should work.
You need the six cyl. bellhousing for the trans, the bolt pattern is different than either the 4 or v8. C4 and C5's are commonly availalble.
The throttle linkage, fan shroud, etc are also 6 specific.
If you find a donor car, which should be easy, it could be simply done.
Not sure why, but I dont understand 89 Caprices with 24 in wheels, either.