Fabion, where is the oil leaking from?????
If you have the yella-terra rocker arms & the leak is from the left rear of the head area you will have to plug the oil passage in the block with a 5/16" set screw to keep full oil line pressure from the left rear area of the block to head area. Cause your top end oiling is via the pushrods.
However if you use the stock type rocker shaft oiling system you still have a head to block leakage issue which is rare.
If you milled the head make sure you grind the slot in the head where the oil enters the head to stock type configuration. Bill