Distributor Gear - stripped?

Been driving 69 AMX for a couple of months with a 1978 Long block 360 recently installed.  I took the old distributor out of the 390 and put it in.  All has been pretty fine, i.e. it has been fast and starts well and runs smoothly UNTIL I downshifted on the way home from 4th to 3rd at about 45 mph.  The car backfired a bit then died.  After towing the car home, I found I had spark and fuel so I put #1 at tdc and pulled the distributor cap.  The rotor was not anywhere near #1.  I pulled the distributor and the gear is very rough and worn down on several of the teeth (see picture).

Was putting the 390 distributor into the 360 an error or is something else going on?  This is a 42 year old point distributor.  I don't mind having a point distributor.  I'd appreciate any comments.

Yea, you probably should have switched the gear from the '78 dizzy over to the '69 dizzy.  Also when you swap them like that be sure to coat the gear with petroleum jelly.  Now, all of that gear material is ground up and has gone through the engine as a oil slurry.  Not good.  I would be tearing the engine completely apart and cleaning everything.  I had one like that and I had to replace all the bearings and get the block honed again. 
What does the '78 distributor gear look like?

Edited by SC397 - Jul/09/2011 at 9:20pm

How did all the engines run millions of accumulated miles without a crutch and not wreck a gear?

Looks at the gap between the washer and the end of the distributor. Even used gears need to find a pattern but you hit the crap lottery with that distributor. The gear gets pushed up and tries to wear into a good pattern and because it was in a slightly different spot it wore through. Very common though.

Sometimes it's cam walk that causes the gear breakdown too. A cam retainer with correct gearset during rebuild is not a lot of extra money for peace of mind.