As pointed out the CUCV alternators have a tachometer signal already. Some vacuum pumps generate a signal as well. But, that signal might or might not talk to your tachometer or TCM.
Your transmission control module should generate its own engine speed signal because it gets the input shaft speed reading from the sensor inside the transmission. At least my Compushift TCM works that way. However, it won't export that signal to a tachometer or its own read out.
I have used the Dakota Digital converter box to go from a CUCV alternator to an Autometer analog tachometer on my M715 with a CUCV engine and dual alternator set up. I also used a Dakota Digital converter box on my Cowdog Suburban project. I have a Delco CS130 serpentine belt alternator on that truck and used the Dakota Digital box to get a good tachometer signal to my gauges and for read out on the TCM display.
If you get a diesel pulse adaptor for a digital timing light with RPM read out. That will give you an exact engine RPM that you can adjust the Dakota Digital box to get your tachometer exactly dialed in.
A Snap-On MT480 or MT1480 "Lummy Mag" timing set up will also give you an exact engine rpm from the slot in the harmonic balancer as a baseline to set your tach or TCM.
