Ok, here's a TCS solution (maybe).
This sensor:
https://jagsthatrun.com/products/speed-sensor-4pac
It has a pass-through, so the sensor goes on the transmission, then your speedo cable goes on the sensor. You keep the stock Speedo, odometer, and the cruise control will still work.
Wire that sensor to VSS+/- pins on the side expansion connector and pull the pin from the harness plug for the stock sensor (pin A10, dark brown wire). Then open up the ECU-GN and remove the VSS jumper ( in the jumper block right next to the expansion connector).
Now, assuming you've got a front wheel speed sensor hooked up to the AUX VSS+ terminal, you'll get into the shaft and gear settings screen and set it like this:
You need to know the actual diameter of your tires and your final drive ratio (don't use 3.73 if you still have 3.42s, this is for my car!)
With this enabled, spin the axles by hand while watching the VSS inputs in tunerstudio to make sure they work, then road test it.
If the sensor work and are reading correctly, then you can move on to the next step, enabling TCS:
All I did here was enable it, change it to VSS %slip, and set the slip threshold at 10. Everything else is default. You can make the CE light blink if TCS is active if you know which output the light's on (Bob? Eric?)
These settings produced a VSS signal from both sensors that tracks perfectly, though there's ~ a 2mph difference in the reading. I'll have to see if I can tune that out by messing with the smoothing settings.
Now, does it work? Well, it does something:
If you look closely at the bottom chart, the white line is actual spark advance, the red line is what the the ignition table is asking for. You can see that when I broke the rear wheels loose, even though the ignition advance from the table was asking for 23.5 degrees, the TCS system pulled it down to 3.5 trying to kill enough power for the tires to grab. This was a brake-stand burnout, so there was no way the thing would recover until I lifted. I just did it to see if the ECM would respond. Actually making it work to get the car to go faster is going to require track testing.
Now, apparently there's a danger here of a stock ignition module losing sync in this kind of situation. I have a TR6, I don't know if it'll have a problem or not. Bob might be able to shed some light on it. This is bleeding edge folks, so try at your own risk.