Which heads are best

Given the pistons are flat tops at zero deck- I'd suggest you stick with the factory type 340/360 X/J/O type open chamber deals, have them redone for performance with a combination of a good 5-angle valve job and some port cleanup, and run those. If you use anything closed chamber you will have detonation issues with the cam you need to run the power brakes with. It will be horsepower limited but will run pump unleaded from anywhere and make decent torque. You really should use dished pistons if you want to use a smaller cam and modern heads but it's a moot point now. Another thought is the open chamber RPMs. IMO a lot of money for the weight loss, bling, and no quench but the iron wouldn't have quench either.