The flange where the distributor housing rests on the block is just a little too far down on the housing for the oil pump drive to engage properly. I machine it off, and fabricate a collar that's adjustable so the engagement of the drive gear and the pump drive can be adjusted properly. Mine also incorporates a squared-off spot with a bolt hole in it to use the original hold-down bolt to secure the dizzy to the block.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!