A 350 can make great streetable power, get a good set of heads, mild cam, better intake, carb, headers, ignition. It really responds to the same tricks as any other brand engine. Most people go to the 400 or 455 since it's cheap torque to change cubic inches and most 60's muscle cars are becoming cruisers only and the bad milage, rough idle are fine for that. (sorry guys but it's true, I did say most, not all)
But for a good driver a mild build on a 350 is a great choice. I ran the #17 small valve heads on a street tuned 350 for years and loved it. Pump gas, nice throttle response, decent milage. You should be able to get 320-350 hp from it easy. Talk to Edlebrock for a Cam/intake/carb package for it. Add Headers and an aftermarket ignition and you should be there.
A bigger engine is not always better, unless that's what you want.
Wanting a Custom fit in an off the rack world.
I don't have time for a job, I just need the money.