Not long ago I was having some major work done on my '64 Nova, and the guy who owned the shop told me that he had a line on a 5-speed trans for about $400, so I told him to buy it and put it in the car. Unfortunately, he apparently wasn't aware that there were both electronic and mechanical speedometer connections on a T-5 depending on when it was built, and didn't figure out that the trans he got for the car had an electronic speedometer connection until AFTER it was in the car. So now I have a 5-speed Nova without a working speedometer.

There are two options that I know of. One is to get an adaptor, and the other would be to find an older T-5 tailshaft housing with a mechanical speedometer connection. How much of a problem will either of these solutions be, and does anyone know where to get an adaptor? I can check with local trans shops about the tailshaft housing.

And has anyone done one of these conversions to change the electronic speedometer connection back to mechanical?

There is more to it than just swapping tailshafts, the gear that drives the mechanical speedo will not fit onto the mainshaft of the electronic tranny. So your best option is to find the adapter that converts the electric pulses from the current tranny to the mechanical cable setup.

The conversion box is called Cable-X. LINK

You could also use a GPS converter but I'm not sure if they make one that hooks to an old school cable speedometer.

If you find an S10 tail housing with a cable connection (1988 and earlier S10, Sonoma and S15 trucks) then the tail housing could be swapped and the VSS reluctor wheel removed and replaced with a drive gear. If the location is different than the machined area on the main shaft, then a shim can be used to build up the thinner area of the main shaft so the drive gear can be mounted at the proper location.
Photos are of a T5 main shaft with VSS reluctor wheel.