Electrical people, how feasible is this? - old marine tachs

So, you can find vintage boat tachs on eBay for pennies.  What you can't find is the control box (seen in this particular eBay ad https://www.ebay.com/itm/114191931641 ) as they remain with the boat or the motor or whatnot and get trashed.  With the control box the price just skyrockets

I know someone could figure out how to get the tachs to read with a coil input or something, but that someone is not me.  Anyone have the slightest clue how to do it?  I have several of the tachs that I've bought before I realized that they didn't have the control box, and one setup that has the control box as well.  I can read a multimeter pretty good, but there's a reason I didn't go off to be an E.E.

If the price point was right, it could even be a small source of income?  I know an arduino could be setup to get it to read, but I'm not sure how much that would be Vs a custom built circuit.

Airguide is a popular tach, and the motors they hooked up to were usually 2, 4, or 6 cylinder 2-strokes.

What if you found a source for cheap tachs in the junkyard and stuff the guts into the boat tach?  Might be just as much work getting it to recalibrate for the different faces, though.

Might be worth a shot to try and find some with a similar arc to them.  IIRC, 70s F-bodies had individual gauges instead of the more modern all-in-one printed circuit dash panel.

Maybe?  I don't know enough about tachs in general to know how feasible that would be.  I wouldbet that the difference between a 6 or 8 cyl 4-stroke and a 2 cylinder 2-stroke would give headaches, though.  Maybe a 4-cylinder 4-stroke?  Or do I have that backwards?