Mopar 493, you stated that you have .010 end play on the distributor, could it possibly be too tight? The reason I ask is because I work in a engine machine shop and the guy who assembles the engines took a sbc/bbc aluminum distributor housing and measured it at room temperature and then put it in the oven and heated it to around 225 degrees and the overall length of the aluminum housing grew around .015" if I remember correctly, so I am wondering if when the engine gets hot there might not be any endplay left on the distributor shaft? I know that the sbc/bbc distributor setup is a little different from the mopar setup but it might be something to check. I would take and bolt the distributor in the engine and measure the end play cold and then measure the end play after the engine is hot to see if you still have end play if not then you could possibly be forcing the distributor gear down against the bushing in the block and causing problems that way. Just a thought.