I posted something a little while back asking about parts interchange between the regular vacuum advance distributors and the MP tach drive. They're made by different companies. You might be able to swap the entire mechanism over from the vacuum unit but I never tried it.

I've also wondered if a mechanical tach can be converted to electronic. You'd basically keep the tach face, needle and housing and replace the internal components with electronics.

There's a guy on Ebay (gaugeguy maybe?) that takes your older electric tach or gauges and updates them with new circuit boards so you don't need a tach adapter. Maybe he could tackle that job. Just a thought.

Not sure if you want the cable to be visible for the 'look'.