[cadillac_al]

I don't think that gear clearance is going to make much difference on the intake mounting part. If anything it would be best to have no shims in there with the problem you are having. When you drop the dist in place, how much of a gap do you have between the intake surface and the distributor sealing surface? If the gap is big, something is out of spec, I would fill the gap with nylon washers and drive it.