With all bolts and the cam chain removed from the issue, then the head should lift right off the barrels with minimal effort. If they don't, I'd go looking again to see what else is holding it that I missed, (like another head bolt). I've gotten my lunch eaten more than once by forcing something like that and then find that I missed a bolt down in a hole or hidden in some manner. Now if the pistons are stuck in the barrels, that is another matter. I have seen pistons destroyed while trying to drive a piston out of a rusted up cylinder but that "shouldn't" have anything to do with the removal of the head As Nathan said, keep that cam chain tight and pulled up out the top or you will be finding what it is like to split a case to retrieve it....... an thet tain't no fun.