I’m putting an AW71 from a 1993 940 into a 122S. I have all the bits and pieces I need except I haven’t decided on the best way to effect the speedometer function. This model of AW71 doesn’t have a mechanical speedo so an alternative is in order. Being an electrical engineer by training, I’m leaning towards an electronic speedo, likely driven off the output flange of the tranny using a Hall effect sensor.
However today at the local pick and pull I came across an AW70 in an 1984 240 with a mechanical speedo. The rear extension housing is the same length and bolt pattern as that of the AW71. However the output splined sleeve/flange is attached to the output shaft with a bolt and washer whereas the AW71 output flange is attached with a large nut.
Therefore I have the following questions for this group: Can I replace the rear extension housing on the AW71, including the output splined sleeve/flange, with that from the AW70? From what I understand about these transmissions the output shaft of the AW71 would have to remain, therefore the spline and O.D. of the output shaft of the AW70 would have to be the same as that for the AW71. Can I use the large nut currently used on the AW71 to secure the AW70 flange?
One additional benefit of swapping the rear extension housings is that I would get the early, smaller u-joint pattern, which means I could retain the front u-joint of the 122S driveshaft. Otherwise I will have to graft a later model u-joint (which I have) onto the front driveshaft of the 122S.
The collective wisdom of this group is deeply appreciated.

Cheers,

Barry