Useable parts from '88 5th Ave. ???

RE: exhaust manifold. Right side is no problem. If you have power steering the left manifold will not work. Too bad, as they are much larger than the stock A body manifolds.
You should be able to sell the 8 1/4 rear if you don't use it. As mentioned, it will adapt to the A body.

Don't get rid of your A body parts yet... from my experience (with a '72 Duster) the radiator would not fit, the engine was not a roller cam and it had a lean burn distributer on it.
C