Hey, friend...... I may can answer a few of your questions.......
Finding some trucks on craigslist will give you an idea of what people may be asking for them, and in what condition. There is a site called searchcraigslist.org just type in "sweptline" and you get all results with that key word..
They put a couple of "hot rod" packages on these trucks, which are pretty rare now. One was called The Dude, it had a 383 but were all long beds. Another was called the Custom Sport Special (CSS) also a long bed, but had a bigger engine than the Dude.......
I used to own a '71 Short box sweptline, and wish I still had it......... loved that truck!