well, got the Z back together today, but there's water leaking in the 4th cylinder again! I don't know what it could be, I've ruled everything out except for the block, considering the fact that I've had this same leak on 2 blocks. What is the chance that both blocks could be cracked?

My dad said that I should try retorquing the head bolts after the car has been warmed up, because that's what he used to have to do on his v8's that he built when he was younger. Would this actually help me out at all?

What are the chances that both blocks could be cracked?

 

i'm starting to think you dont have a a flat block,in another thread you said you found the head to be warped?if so then there is a chance the the mating surface of the block(where the head meets the block) might be a little warped.
take a good striaght edge,and a feeler guage and check the surface to make sure there not a huge diffrence on the ends.if there is thats most liekly were your prblem is coming from.