coopers O ring headgaskets are one of the strongest you get get!what is the exact problem,you say you have pressure in the coolant!i doubt very much its a headgasket problem as it is very rare for the fire rings to fail!usually they just fail the way mine has!but yes they are alot of money as i am thinking of going to a 200 block,but u can not simply swap everything over fella you would either have to get a complete good ready to go 200 block or rebuild one!you do not have to replace the fire rings by the way you can just replace the gasket!but is it worth the risk!have you checked out all other posibiltys?i.e thermostat etc?have u had your coolant sniff tested?