Blykins, Im a bit mystified about your 5/16" FE drive- ARP only list one & its 1/4" hex, plus in order to convert to 5/16" the pump gears plus Dist shaft would need to be upgraded as well along with possibly enlarging the spigot in the block to accept the larger dist shaft dia @ that point. Not doubting your info, just interested as its something I have considered doing to the odd FE & useing a shortened 429/460 drive when I know the customer is going to break all the rules & jazz the throttle when the
oil is still cold.