i have a 71 383 and my stock pistons are down in the bore .090 at tdc . i milled a set of 346s .055 and they came out to be 76cc chambers. using the shim gasket i calculated my comp. at 8.8 to 1 . better than the 8.2 or 3 it was . i think you would be better off with those stealths on the 383 than the iron heads.