Generally, only the HP 440 and Hemi had 4-pinion planetaries both front and rear, the exception being when the HP 383 used the same trans as the HP 440. The 3515846 is 383 only.

The factory parts catalog is a better source of correct parts for a particular trans, the FSM is more general and not always correct.

Removing the wall from the check ball pocket creates a smoother path for the fluid that feeds the 2-3 shift valve. In stock form the fluid leaves the 1-2 shift valve, travels through the separator plate to the transfer plate, back through the separator plate to the 2-3 shift valve cavity. The direct route causes less parasitic loss.