I agree with everybody's opinions here.
YES...It will most likely never sell for what you have in it after a total proper restoration.
YES....I feel a fully documented, numbers matching, correctly restored black/black 340 4spd car is worth $60K-$70K in today's market.
YES....Being a black/black 340 4spd car, it's worth doing and doing right. Not many cars like that are receiving the quality resto they deserve. It needs to be put back to 100% stock original to maximize it's value.
YES...If you've had the car a long time and the car "owes you nothing" or your investment to date is next to nothing, then spending $50K-$60K to make the car 100% brand new again, won't be to hard to get your head around. It's when people pay $20K for a project, then realize the cost of restoration....that's when it gets scary.
YES....My complete ground up stock restorations cost around $50K- $60K CANADIAN without major metal work. That's about $45K USD right now.
YES....You need to find a quality shop that turns cars out at a good rate without costing a fortune, there's not a lot around.
YES....Make sure your son is well insured before driving it to the prom