833 behind a stout 440?

I was under the impression the 440 6-pack cars had 18 spline units and maybe A12 cars, not all 440 4 speed cars, could be wrong and always up for learning something.

I think if you are really that concerned, you can just get a HEMI input shaft. I think the rest is the same. The HEMI cars would twist the 23 spline units, hence the more stout 18 spline units.