Mechanical to electric spedo

[Rifter_Chevy]

I want to convert my mechanical spedo to a electric spedo because im going to install a new custom cluster and autometer doesnt make a mechanical spedo in the series of guage i want to use.

I have seen links before to gears that convert the mechanical signal to electric but cant seem to find one now.

Im running a TH 400 trans and a 208 transfer case but will be running a 205 by the time i do this swap so if the gears are differant i will need one for a 205 t case.

Thanks guys!