You start dicking with heads and what not on a block that's not made for it and you're going to wind up in a bind.
friend bought a highly modified motor that is "stage 3"(what ever that means) and has had numerous problems with it. it reinforces my philosophy of keeping engines stock cause that's how they were designed to run. when you start tweaking engines to the top level of performance it sees stresses that it wasn't designed for. in short KISS is a good motto that i live by.