Can't get distributor to lock down.

[grubsster]

I am having a fun issue. I have installed many distributors with no issues. I had my engine rebuilt a few years back and have constantly had timing issues. I thought it was an internal distributor problem and chased that for a while, then purchased a GM branded HEI from Summit. Dropped it in and have been driving it but still having issues. The other day while replacing plug wires I bumped the distributor with my hand causing it to move. No matter how much I tightened the hold down it still moved. Bought a fancy Edelbrock hold down with a stud and still moved. Bought the the moroso shim kit, removed the distributor and checked to see how much gap between the base of the distributor and the intake which was about .025. Installed the thick shim from the kit which checked about .065 and the gasket. Also got an OEM hold down from the salvage yard, used a stud so I would know the bolt is not bottoming out. Snugged up real good, let it run about 10 minutes after timing blipped the throttle and sure enough it rotated. I have not tried what another member on here did, which was to tap his oil pump shaft and his seated, which I will try tomorrow. I have pulled my 3 remaining hairs out. Any help would be appreciated.

Engine is a 283 with vortec heads and Edelbrock intake built by Boyettes machine shop in raleigh, a very reputable place.