A friend has the head off his 225 to fix an oil leak. The only reason he has the truck is to abandon it at the airport terminal when he is flying. As such, he doesn't want to spend any unnecessary money on it.
It's a lean burn hydraulic motor. Compression was a nice even 135-139 psi on all 6.

Other than accounting for the difference in head gasket thickness how far can he cut the head without having problems with the hydraulic lifters?

It would be nice to get a bit more compression.