If you've got the speedometer cluster, you'll just need to repin the cluster connector, add the VSS wiring (looks to me like an S10 or Astro will donate the wiring and connector, they seem to be the same) and get/power a DRAC, again an Astro is a good donor.
Once you get that setup, calibrating the speedometer is as easy as soldering some jumpers on the DRAC board.