Looks fun. I have no idea on valuations though. Do you really want something like that? Skylarks have considerably less mass apeal than Chevelles. A Cutlass is the same. That is the top dog one. I'd make sure it's a real GS if that's part of the valuation. Not hot on the black and orange but looks ready to go as is (add rings, which is a little scary).
I started pricing out my build and it was around $15k without getting really crazy. Life got in the way. I'd still like to do something with it, but I need to get a place to work on stuff first.