Horsepower with mileage options

I would agree with the 3.55 gear ratio being a good balance for getting the best of low end off the line with a balance of it drinking fuel. Provided of course a lighter foot on the pedal, accompanied with a 4bbl carb and intake combo, 258-268ish cam, dual exhaust, and an od transmission would get it in the range of a semi economical rompity car.
Besides power and mileage, there's another aspect that can be very satisfying to have in an old car, and that's good handling.
Especially for a young guy he might like a good handling car that can take corners and have it handle like a more modern car.
I definitely think handling should be on the list of improvements.