There should be no end play or up and down movement on that engine, the crank bearings should be a light press fit in the cases, they do tend to wear out the bores in the cases though, pretty much junk at that point. The bearing on the drive side of the crank is what holds it in place. Also on those cranks they wear the journals where the bearings seat and will move up and down if worn out, the bearings should be tight on the journals. What happened to a lot of cranks is when the rod kits were no longer available they started using a later model rod, the crank pin was larger so they ground down the ends of the crank pin to fit in the crank, they made the pin weak by doing this and the pin would not stay in place, so they got the brite idea to weld the crank pin to the crank, when you do that you can't true the crank and it wobbles in the bearings, that causes them to wear out the bearing bores in the cases and ruin the journals on the cranks. I have also seen the weld break off and go through more than one engine and ruin the cylinder. The correct fix is to bore out the pin hole in the crank halves to accept the larger pin, that requires precision equipment, something most shops don't have
