[ray_mcavoy]

With that tach having the terminals marked "Ign Sw", "Dist", and "Grd", it will have it's own internal electronics and not require a transmitter box.

As you mentioned, the older tachs that just have the 2 terminals marked + and - are the ones that need the transmitter box.

I don't think I've ever seen any sources documenting the OE-x model numbers for the factory installed Sun tachometers. But I know they did have a few different ones for 6 vs. 8 cyl as well as standard vs. transistor ignition.

The old GM parts catalogs list the following numbers for 63-66:
GM #3852111 for 6-cyl gas engines.
GM #3839947 for V8 gas engines with standard ignition.
GM #3885480 for V8 gas engines with RPO K66 transistor ignition (only available in 1966 medium/heavy duty trucks).

Unfortunately, they don't show any cross reference to the Sun OE model number that's indicated on the back of the tach. The few examples I have seen in person were Sun OE-6 models that also had "8-cyl 12 volts" printed on the label (where the one in your example just says "Sun Electric Corp"). And they were also printed with "STD IGN" directly below that, which would indicate a match up with GM #3839947.