I'd make sure it IS going all the way down. Use a long thin screwdriver or a small rod that will fit to the bottom of the slot in the oil pump shaft and mark it even with the block distributor hole surface. Now hold one end of that marked rod agaist the bottom of the distributoe mount flange and see if the mark is shorter or longer than the end of the shaft. If it's longer then it's not going all the way down and if it's shorter then the dizzy shaft is bottoming out in the oil pump drive and not letting the dizzy seat. The factory 235 dizzy has a collar that you can loosen a stovebolt and adjust the height.

Evan