I lost a distributor gear on my FE. I had a couple of problems that added up.
1.) I installed a roller thrust bearing from Ford Power Parts for the cam. Unfortunately the supplied beautiful 12 point bolts were a bit too long and one of them partially cut off
oil to the bottom of the distributor gear. Extra drag on distributor leading to more tooth load. Not sure if your motor has a similar
oil passage setup.
2.) Distributor I used did not have proper end play. When distributor is installed in the engine the gear is supposed to bottom on a machined face just below the gear. As the cam turns the distributor it trust the gear down against this face which is feed from the
oil mentioned above. If the distributor is not mounted in the right position the thrust will be taken by the little bearing in the top of the distributor leading to more drag and tooth load. Look for small shavings, etc. in the distributor under weights. This can be checked by measuring the dist. shaft endplay on a bench and in the motor. The endplay should be less by several thousandths when it is installed in the motor showing that the gear is contacting the thrust face. Who normally checks this?!?!?!
3.) Overly high initial oil pressure due to incorrect relief spring in by pass. Leads to extra load on teeth.
Add all of this up an you get a wiped out gear in ~30 minutes. I noticed oil pressure low and shut off motor. No damage, BUT fine particles of ground up teeth EVERYWHERE. I did a complete teardown and clean and rebuild. Lots of fun.