Yesterday I put the bottom of the 312 togeather. Got the pan and oil pump all bolted in place and then tried to install the pump drive from above. Was the pump drive shaft suppossed to go in from the bottom or can it be dropped down from above? Seems the retainer clip on the old shaft wouldn't let go down through the block. I have a new billet shaft for it, is that supposed to have a retainer clip on it also?