Anyone have any experience with hard starting with the GM Vortec 4.3 in a 52-6FGCU35?

It wouldn't start so I checked the Impco regulator and found it full of corrosion. I replaced it and found that the engine was very hard to start. It would crank and if I let go of the key, the engine would suddenly spin over backwards and puff out the air cleaner housing.

I moved the distributor to where it would start easily but I could see the engine stall for a split second while cranking, almost like it wanted to turn in the opposite direction.

Someone mentioned a spark delay module that Hyster, Clark and Cat have used to prevent starter damage, but would that be what I need in this case? Anyone have any fixes?