I'm looking at building a 383 in the future. The question I have about the block is whether to utilize a block with a one piece or two piece rear main seal. I will likely have my choice as I will be starting from scratch.

 

Get a 1 piece. Much easier to maintain and you dont have to pull the crank for a new seal. make sure to get a 1 piece pan and flywheel

 

Idk if my opinion is correct, but from my experience 1 piece is less likely to get a leak.