Picking parts should be a lot closer to the end of your process. If you pick/buy parts first, you are highly likely to wind up disappointed in the result (and how much money, effort, and time you spent getting it). It's possible for a 1bbl Slant-6 in good condition and proper tune to be plenty peppy around town…with something other than a 2.76:1 rear axle (standard equipment starting in '68) and big tires (evident on your car), for example.