A company called jaguars that run (jtr) sell a motorized cable driver, with a controller for an insane $300.00-$400.00 bucks. Or for around two and a half c-notes you can buy an autometer elect. speedo (self adjusting), or You could maybe try fitting a mechical drive to the tail shaft housing ( difficult, not certain to be possible). Or you could install a tach, and with some math get a pretty good fix on your speed! Maybe there's other options as well?
