On the OldGMC site, there is a blow by blow description of the procedure. There is a seal marketed by "Best" gasket which they claim is better than the others. It is supposed to have teflon etc. involved somewhere in it's makeup. I replaced mine and it was perfectly dry for about the first three hours of running and then it started to leak. I was tearing down my motor at the time and as an experiment I tried to remove the upper half with the crankshaft in place. I was not able to budge it at all. This is not always the case but it was my experience.
