If you don't have an aftermarket block to not only have the added strength but also bore size then I think your wasting your time with these and or similiar or even better heads.
I agree, with a factory block you're limited by block strength, regardless of what head you have. My 408 used a 71 cast 360 block and ported Edelbrock heads, when I tore it down to freshen the main and cam bearings showed signs of block flex, at least that's the only explanation I found. I had posted on another forum about my issues and a member there contacted me about a Indy headed, R1 engine he had. I bought it and built my 434.
