Your
oil pump seized before? Do you have a mesh screen strainer? They should prevent peices big enough from seizing the pump to get through.
What about the length of the
oil pump shaft or the dist body, if they were too long you might be able to tell when you tighten the dist clamp, can you get a feeler gage between the top of the block and the part of the dist that seats against it?
Was you gear pressed on or was it loose on the shaft before you pinned it?