Good morning gentlemen,
the tach is military, not sure what it is out of. Truck applications would probably be driven as has already been mentioned, most likely off the distributor or in some cases off the cam. If this is out of a radial engined Stuart, I would guess the cable drive was from the input shaft on the transmission up by the driver, the same set up the Shermans used. On the twin V8 Stuarts, I would think we would be back to drives off the distributors.

Perry