Joe:
That's the drive I referenced in my earlier post. It is essentially an AC generator and produced a sine wave for the early ECMs. That signal has to be rectified to give you the needed on/off signal to ground that is required to drive a conventional tach.
Tried to find the circuit on my computer but it didn't survive numerous crashes over the years.
The link I sent you regarding the circuit is only available in the members area. Money really well spent. The archives and articles will make your life much easier. Lots of 6.2 info there.
Good luck
Bill
91 Buick Roadmaster/Avant 6.2 NA conversion (gone but not forgotten)
94 Cadillac Fleetwood (sold)
08 Aerolight 23TT
06 Vortec Max Silverado CC SB (sold)
10 Avalanche (electronic quagmire but love the truck)