On a 74 Duster with a 904 Trans.........My rear end had a small tag with 2.71 stamped in it identifying the gear ratio. My question is my rear end cover is a 10 bolt, with no drain plug except for on the very top of the rear end just before the housing. I looked at the rear end I.D. guide listed in the the tech section but it does not show mine. Anyone got any clues what size this could be?