The distributor also turns at half crankshaft speed. If it's binding in one spot every other revolution of the crankshaft, I'd put money on it being a buggered up gear . . . either on the crank, the cam or the distrbutor drive.
I don't know jack squat about a type 4 engine, but the softest metal in all those gears on a type 1 is the distributor worm drive gear on the crank. I've buggered one of those installing a distributor drive on a type 1 before. I probably should have replaced it, but I just took the block back apart and doctored up the gear with a small file.

It worked fine and never gave me any trouble after I put it back together.