Edelbrock / RHS heads, or go BIG block and put it to bed!

He really needs to get rid of the taxi cab carb... it's probably a good 15hp behind a similar sized holley. I'm not a fan of those Ede carbs, period.

No reason with good tuning, a really good converter and tweaking, that car can't run 12.5's as it sits before any head change. Just takes time and finding out where the time is going. I'll guess the converter isn't the best piece, change that and the carb and it's an entirely different animal.