It's tough to give a short answer. 6k will be tough for a fastback. It'll depend on how much you want to do after. Rust is your worst enemy, floor pans, trunk floors, front frame rails, rear leaf spring mounts and cowl vent leaks. At that price your best bet would probably be a a disassembled frame off, where all the rust has been repaired and replaced after sandblasting. Then start from scratch. It'll take a longer time to get to driving, but it'll be a better car. It's tough to buy a car that's stripped to nothing. Bottom line - engine, drivetrain and interior are easy things, fighting hidden rust and weak metal is a constant pain. Go for the best body even it's doesn't come with an engine and tranny. Good luck!
chevy runs deep, Don't step in chevy!
289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.