Location for driveshaft speed sensor on Subaru GC8 (Type-RA 1997)

I was a pinch close to find a space on the driveshaft to place a driveshaft speed ring, but I ran into a blockade: A slightly raised knob won't allow a speed ring to be seated flush on the center diff slip yoke. Furthermore, there's no place on the rear diff pinion yoke for a ring to be installed.

Has anyone had success mounting a wheel speed ring on the GC8 driveshaft?

If there's no chance of it happening without modification to the driveshaft, what are the other alternatives? (Would prefer to not use GPS, but not ruling it out just yet.)

Any help would be appreciated.

Contextual details:

Vehicle: MY97 GC8 WRX Type-RA STI

Problem with the front diff slip yoke: There’s a little knob that’s getting in the way for the speed ring to sit flush against the yoke. That area on the knob offers 5-6mm ring height and ring internal diameter (ID.) of 2.3819in (6.06cm). Good news is there's a ring that may fit. It’s 2.375 in (6.0325 cm) ID. See pics 1, 2, and 3. The green line |█| shows the workable area. The orange line |█| shows the non-workable area of the yoke (diameter is too large).

Rear diff pinion yoke: There appears to be no space for a speed ring. There’s a shroud covering the tubular parts of the yoke that I think would be perfect for mounting the speed ring. No pictures available at this time.

Do you need driveshaft speed for a particular reason, or are you just wanting to get a vehicle speed input? I had a similar issue with my RA, I resolved it by getting hubs from a later model (2000 GC8 if I recall correctly, it was a while ago) that had the ABS tone rings and wheel speed sensors installed, and used them instead.

I agree, way easier to swap to late model GC8 or even early model GD STI shafts. So long as they are both the R180 rear diff (both 6 speeds) it should all bolt up then use the ABS sensor as your input

No other reason except for wanting vehicle speed input. I intended to use it for launch control but learned that AWD requires one to use RPM or GPS.

To clarify, do you mean getting a 6-speed driveshaft that is compatible with R180 rear diff, and also getting hubs with ABS sensor?