It could be a cylinder crack or could be a warped head. Were the base gaskets changed too?
I would get a straight edge on the head and check it. If it's out a little, it can be sanded flat on a sheet of fine grit sandpaper placed on a very flat surface. Sand in a figure 8 pattern and keep even pressure on the head. Check often so you don't do too much in one area and ruin it.
If it's out a lot, you can find a good used one for pretty cheap.