[Elmopquackenbush]

If you replaced the Oil Pump / Distributor Drive Gear and it is not fully seated as shown in the attached picture, it will prevent the Distributor from sitting flush with the top surface of the Engine Head by the same amount of gap.

This happened to me when I replaced the Oil Pump / Distributor Drive Gear in my 1930
Model A pickup Truck.

I had to turn the engine over by hand using the Hand Crank Tool and that allowed the Oil Pump / Distributor Drive Gear to properly mesh with the gear teeth on the Cam Shaft.

Doing that made the Oil Pump / Distributor Drive Gear drop down and sit flush with the top surface of short boss in the Engine Block Oil Gallery.

Now the bottom surface of the Distributor sits flush with the top surface of the Engine.
Make sure that the Guide Pin on the Distributor sits into the corresponding hole in the Engine Head.

Hope this helps,
Elmopquackenbush
1930 Model A Ford Pickup Truck