I only know of one motor that has non interfering heads, the toyota 4AGE. are our motors like that? you know, like it the timing chain/belt breaks there is enough clearance between the valves, fully extended, and pistons, TDC, that they would not collide. I personally dont think they are. Is it as simple as putting a spacer between the heads and block, with all the correct cooling passages and correct sizes for the pistons, that we could too have a non interfering head? oh, we would also need longer pushrods too. has anyone thought about this problem? maybe it isnt a problem, maybe just a problem in my head....hmmm