A friend put the fastburn heads on his 350 and it made a huge difference. He also had to buy a new intake though. I think its the same with the Vortec Bowtie heads, which are the cheaper cast iron version of the aluminum fastburn heads.

The thing with those heads, aside from the valve sizes, smaller combustion chamber and other things is the heart shaped combustion chamber which causes the air to flow in a certain way.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi