Mercedes 722.x I.D. needed

Figued I would post this here and it'll get more traffic than my build thread. Cliff notes: I bought an 83 W126 300SD that ate its timing chain. That OM617 and its 722.3 were pulled at the same time. PO bought a running OM617 with a 722.x out of an unknown Mercedes. He does not remember what body style, and this is the only discernible difference I have seen thus far, aside from the donor running a KKK turbo, and the original running a Garrett. Here's the problem: Donor drivetrain has this on the transmission:

Whereas the original drivetrain does not:

If need be, I will swap transmissions, but I'd prefer not to if possible. Does any one know the function of this part? The wire leading from it was electronic.

Any help is super appreciated.

My WAG would be a hall effect trigger counting starter ring gear teeth but why I have no idea.

It's the tach signal pickup, for all of you champing at the bit to find out. Prior to 1984, it was located on the front balancer, underneath the vacuum pump. Seeing as how the donor engine still has one there, I am assuming that someone swapped out the transmission at one point.