I have a custom 55 Chevy 2dr BelAir hardtop SBC 400 with a 700r4 and 4.11 gears. It runs great, a lot of fun to drive....no wasn't built for gas mileage. I like your idea, clean it up, and let him enjoy it this summer. Sounds like it is a cruise night/car show car. It's would be easy to add a little bling to the engine as you clean it up. A little rattle can paint, chrome valve covers and air cleaner doesn't cost much. He can research, ask around at car shows, and with your help decided what he might want to do, if anything.