I'm making this motor into a 383 stroker. I am using stock cast iron 64cc heads. My question is, Can I use a stiff spring on these heads? The cam I've ordered is a Comp Cam Magnum 294-S with a .525 lift. Will the stock heads support a lift of this size? Can I machine the heads to work? Also, I think my compression ratio is going to be a bit on the high side and I want to run pump gas. The pistons I have are 383 Speed Pro forged aluminum part #L2491F30. With the 64cc chambers I beleive it's 10.5:1, is that too high for pump gas? I am learning here so any help is much appreciated!