Keep it class legal Mazz, it's not worth the hassle if someone calls you out. I'd go with the first piston choice and the big dome. I wasn't sure what mine would be until I got the piston, using the cc kit, I was able to determine what thickness of base and head gaskets I would need to arrive at the compresion I wanted. It took two extra weeks cause I had to order the piston, wait for it to arrive, then cc it and order the gaskets after that.
Replace that tempting extra displacement with sky high compression. Make sure you got your head and case vented real well. I think I popped a seal on mine even with it vented pretty well. Anyhow, I doubt you will be underpowered in the 88 class with the combo you've been talking about. Those guys seem to be pretty reasonable with thier motor builds, unlike the higher displacement classes that are out of control. 15hp is so 2007!
