727 shaft endplay

Standing it on the end works fine. I almost always use the thickest washer (.102") and you can not stack washers or pump to front drum alignment might be an issue. The thickest washer is the most you should use. Did you check and adjust the rear drivetrain end play before you installed it? I've never had one that loose unless the rear drivetrain was loose. When the rear end is tight the .102 washer generally will get it a lot tighter than .051"