Sounds like the big block with 4 speed was a mixed bag. It would be interesting to determine if the cast crank 4 speed trucks were early trucks or late trucks. Might be such a thing that Mopar originally thought the cast crank was up to the job and discovered differently, or that the original plan was to use up the forged cranks remaining in inventory until they ran out, then hope the cast cranks were up to the task. I suppose a 3rd option was they started with the cast cranks, were somewhat disappointed with their service life and went to existing inventory until they ran out, then went back to the cast cranks as a last resort.

The possibility still exists that they grabbed whatever was handy on the production line as well. Two things are fairly obvious, nothing was consistent, and what the books say they did is not very accurate. Gene