AMC used alot of Moparts, and Ford and Chevy. Maybe they adopted the Mopar lifter OD (as it was the best) and the lifter manufacturers just determined that one style of .904 lifter will be made with the universal AMC pushrod oiler seats as they do jack (are almost check-valve capped by the solid ball on a non-oiler pushrod) on a solid pushrod motor and do everything on an AMC/Magnum motor. Just economics. Im thinking that motor would be rattling like a can of spray paint with way too short pushrods and they would possibly unseat from the lifter at high rpm valve float. I did a mains and rod bearing change on my back under a car over the course of a week, all kinds of stuff floating around down there but I used 2 cans of brake cleaner on everything before I put it back together and 5 years later when I pulled the caps, there wasn't a scratch on that crank. You dont have to work in a clean room to put a motor together, just make sure everything is clean right before you install it. Cover it with a hefty bag on the stand if you have to take a break.
