McToy

Hi all, I have a late 85.5 944 that the speedometer isn't working on. So I'm thinking no big deal, let me check the connections on the Speedometer impulse sender at the transmission, worst case buy a new one and swap and that should solve the issue, right?
Well, I just got under the car, found the cable connector hanging in the air not plugged into anything...hmm... so then I check where the impulse sender is supposed to be ...and again, nothing.
Here's the mysterious part: I stuck my phone in there to snap a pic and the hole that you see is where the impulse sender is supposed to sit but:

It looks like neither the sender fitting nor the yellow plastic speedo drive piece are there?? OK, but what's really throwing me off is when I look online at the sender fitting pictures (the metal fitting that holds the plastic speedo drive gear in place) they show the fitting has a thread and as you can see in my picture there is no thread at all where that fitting is supposed to screw into??
Here's a picture of the sender fitting, the top section is what's supposed to screw into the sender hole:


Now I'm thinking maybe the PO had swapped an early transmission into my car? But then the hole for the sender wouldn't be there at all...
Anybody any clues how I get to fit the speedometer impulse sender onto my transmission? Any tips that save me from dropping the transmission would be greatly appreciated.

Tx,
Ralph