Panhead Parts-Motor Challange

Our vintage motorcycle friends bring motors to build that have never been "a motor" before.  To get it correct, it's a Mind Trip of spacers, thrust washers, end-play, side-play, stack height, clearances . . . then, when you get it all correct . . . the bearing retainers are aftermarket "junk" . . . and it's a switch, swap, trade, mod, deburring game of switch & swap.  Trying to get all the parts to "like each other" is the hardest part. 
Why can't everyone just get along ?????