I think what you are experiencing is the
oil pump drive preventing the distributor from engaging the camshaft drive teeth. If you can remove the distributor and look into the bore where it goes. in the bottom is a hex shaft that drives the
oil pump from the bottom of the distributor. Do not try to lift it out or try to
remove it. Rotate the shaft about 45 degrees (use a long set of needle nose pliers or a dummy distributor without a gear) and try refitting the distributor, keep turning and refitting it until the distibutor drops right in where you want it.
If this is not the correct interpretation of your problem forgive my long winded solution.
Rick