[storm9c1]

So right now you have a mechanical speedo with a transmission that produces an electronic signal output?

What I did on my truck was purchased a "Cable-X" box from tachman1 on eBay. Do a search for "cable-x speedometer". However, this is an expensive route ($300+). But it's easy to hook up -- 3 wires (12V+, ground, VSS from trans). And some dip switches to determine your pulse rate based on your gear ratio and tire size.

There may be others who know how to swap in a speedo gear drive into the transmission, but it's going to be some work on the transmission side. And I bet this kit is as much or more than the Cable-X.

The final option would be to somehow make a hybrid speedometer in your dash using parts from an electronic speedo.