did you install the threaded oil galley plug that connects to the very front lifter bore on the drivers side (#5) ? this is installed from the front of the block prior to installing the distributor?
If you're not sure...remove the distributor and see if the galley plug is there....you can bend a small wire at a right angle and see if it goes in that hole...if it goes in to the lifter.....you have left it out...oil leak...

George