I talked to Mark, going off the spec for a 8171PT head gasket on the Summit Racing site of .039". I assumed that would leave me .036" piston to head, borderline but pr. He mentioned. 042" was the actual spec. I happen to have a used 8171PT hanging on a hook, it read .042" like he said, imagine that. That should put me at .039" piston to head, about perfect. I am going to polish the iron #6 chambers to 68cc so it will be apples to apples when I swap eventually to the Edelbrock aluminum. That will put me right at 9.5 to 1, should allow a nice timing curve on 91. The only variable will be the new 1.65 ratio(.541" lift) from Mark to 1 vs 1.6 ratio roller tip rocker arms(.525" lift), I also have 1.72 ratio(.564"), I may run but they need checking in the push rod cup area .I don't want anymore delays from this machine shop as the iron heads need .100" milled off the rocker pads to properly run the new rockers. I am probably selling my Performer intake as clearancing may be needed for the roller lifters and limits this combos. Not worth it to run the hot air choke.