This problem began with the failure of the head gasket on the 3B engine that has been transplanted in my 77 FJ40. I have removed the head, everything looks good except that two of the combustion chambers have small cracks. Do i need to replace all of the combustion chambers, or can i just change the two damaged ones? Can the combustion chambers be removed without the use of SST 09208-48010; if so, how? Is there an upgrade that will prevent these cracks from forming in the future?