This is a bit necro but it's only about the fourth topic down so I'm not sure if that's a problem -- apologies if so.
In any case, I'm in the process of planning my own electronic speedo conversion but I don't (necessarily) intend to go with a kit. I have, however, completed similar on an '86 Toyota Pickup with W56 transmission. What I ended up doing was getting the speed sender from a later model version of the vehicle ('93, specifically) and fit it into the gearbox. Also looted the dash and used the speedometer from it; works like a charm.
Which is somewhat the blueprint for this work on my Eagle. Find an electronic speed sender (8 pulse per rotation square wavetrain per elsewhere in Jeeper communities -- the Toyota I worked on was a 4 pulse per rotation square wavetrain so not too odd) and matching speedometer and adapt it to my Eagle. As my Eagle has a worn out either speedometer cable or speedometer and from experience after one goes the other will eat anything new put on it.
Per that resource (and unfortunately I didn't save the link, but some googling helped); basically all electronic speedo models Chrysler built use the same square wavetrain as well, so hopefully it shouldn't be too difficult to source parts from a yard.