OK, here are the instructions if your ABS is working.
I used the Dakota Digital SGI-5 speed signal interface. It works great, simple 4 wire install. Power, ground, signal in (from ABS) and signal out (to speedo)
You want to use output #3 (8000ppm ac output)with switch #3 and #4 up.
For a '97 get the ABS signal from the OBD data link connector (red wire with violet tracer) The factory speedo signal wire (white with orange tracer) was found in the big white wire connector that is under the dash in between the clutch and parking brake pedals.
Since my ABS controller is TU and unplugged, I spliced into the wires from the rear wheel sensor. The controller grounds the wt/vt to ground so I grounded it to the frame. I sent the wire from the rd/vt straight to the SGI-5.
After the install I borrowed a TomTom from a friend and calibrated it at 30, 45 and 60 mph. With the speedo correct at 60 the truck is going about 28 when the speedo shows 30, but is deadnuts on at 75. Good enough for what I need.
I found the Dakota Digital on e-bay.