340 rear main seal leak/gush

So my buddy recently refreshed his motor due to a cam change which included removing the crank assembly(67 Cuda 340 auto), upon reassembly he replaced the rear main seal of course. He also installed a higher stall torque converter, I only mention it because it was a change and probably unrelated to the leak. So he fires it up and drives it to my house a few blocks away(lets not talk cam break in right now :) ) and while bringing the revs up and holding them, a river of oil starts running out of the back of the motor, and not the stereotypical rear main seal drip, I mean this dumped enough oil onto the street that i actually got out the floor dry. His pcv system includes a valve cover vent running to his air cleaner, and also a vented oil filler cap.
Has anyone ever run into this before?? I cant figure out what could have caused that substantial of a leak.