The head I found to replace the cracked one already had stock size exhaust seats installed in it at some point so they needed to be removed before cutting both heads for the bigger exhaust seats that will be installed. Seat removal is done with a cutting bit on the drill press. The head is mounted and leveled then the old seat is cut till just a very small amount of it is left which then spins freely and can be removed.
Here's a couple pics showing the cutting bit that gets lined up on the bit guide which is inserted into the valve guide and then the old seat after cutting and removal.
