What we did was to trace all the regulator and alternator wires out and fixed any previous-owner wiring snafus. We found color coding changes hiding under electrician's tape and such. Example....yellow wire coming off of the alternator plug connected to a black wire and a black wire coming off of the alternator plug connected to a yellow wire all hiding with a layer of tape. Nightmare-ish.
We configured the six wires in the voltage regulator plug to match the engine manual wiring diagram. Our new, Echlin VR550 voltage regulator's plug is not configured the way the manual shows.
The pulse for the tach comes off of one of the stator phase windings. The stator is a wye, three phase stator. There is a wire connected to the output of one of the phase windings in the alternator harness. It was one of the color code switch-a-roo wires. This color code problem caused so much hair pulling, as you can imagine. We got good tach pulse signal, once we got the pulse wire sorted out.
The direct replacement Teleflex tach is a 54314D.
Three plus days chasing funky wiring issues.
Still have an apparent overcharge issue. Plan on getting that taken care of
Again, thanks to you all for your helpful input.