Not only the headers, but also check out the recent hotrod mag article where they did a cam swap in addition to the headers. I believe they got well over 400hp without touching the heads. I can't speak to the upper limits of this motor, but as far as I am concerned, its the first mopar killer smallblock. (at least on stock shortblock)

I am toying with the idea of buying a beater 66'ish a'body to start fittment, and see if I can fit twin turbos in there somewhere. They do it with 5.0 mustangs which are about a'body size... why not go twin turbo Mopar?