Definitely worth considering the head swap.
I agree with Kevin about your ring test but given that you are not in a position to honing the suspect cylinders (if I understand correctly) without significantly more effort the head swap would help idenfiy if the problem was with the head or the block. I beleive you had a coolant leak from a crack (?) in the block which may or may not be part of your problems but it could be that the head gasket replacement will seal that up at least for the short term.
As others have said removing the valves to inspect the guides and installing new stem seals would help confirm if the previous head or the block was the primary issue.
