Last time I replaced a headgasket on my 351 it leaked coolant and mixed with the oil, basically ruining my shortblock. I have a replacement shortblock that Im going to throw in her. This time I have the motor and heads out of the truck. What can I do this time around to make sure its leakproof? Give me every precaution you can give, no matter how small, dumb or insignificant it seems. Thanks stangers.