I am buying a 73 from my dad. It has a Motown limited edition 454 small block motor and a turbo 400 trans. 4:10 rear end and is basically set up for the quarter mile. That isn't what I want to get out of the car. I'd like it to be more road friendly but still have some power. The compression ratio is 10.5:1. Do you guys think it would be okay to run 91 octane fuel in it? If so, could I get away with just changing out the rear end?