Yep, if you really want to know what it is worth, you need lots of pictures. The price range will be related to the details. Could have been really nice back then, or it could have been a bit crude, but at least it sounds like it is still presentable.

I would probably go to a website like the www.jalopyjournal.com (the HAMB). The car sounds like it fits into what they are all about (pre 64 Hot Rod builds). Originally built in 57, OEM frame, updated to a 389 (the old Hemi would have been better, even there), the paint and interior also fits in there. The more of the original 57 build pieces that still exist, if still functionable, would add to the value there. They will look intently at what is era correct, down to the tires and wheels. They love "new finds" of old builds.

How much does the guy want to get out of it? Most old guys have a number that would make them happy to get, though sometimes those prices are not connected with reality. The next thing is how long he is willing to wait to get his price. That car could be worth $5,000, to $20,000 or more. Would be worth the effort to take some pictures.