They were nice cars. BUT to modernize them, it can take a "bit more" than other cars to make happen. TorqueTube drivetrain is one big deal which restricts a lot of common "street machine" things, unless you change the rear axle, rear springs, and trans. DynaFlow is "smooooth as goooo", but the few 3-speed manual trans cars performed much better. Brake master cyl is still under the floor, which limits upgrades, too.
Check out videos from "Reality Rides" where a shop rebuilt a '55 Special. Quite neat.
Given the above-mentioned "limitations", you can still make a neat car using production architectures. Back then, and probably up until the middle '70s, almost everybody either had "rich relatives", neighbors, friends, car pool mothers, or such that had a Buick. Even if their immediate family didn't own one.
Enjoy!
CBODY67