Most of the old SW tachometers have the terminals marked a little better. Of course when I think old, my thoughts go back to the 60s & 70s. They generally always have a POS & NEG terminals for electrical power & return then a SIG terminal to connect to the distributor breaker point side of the coil. They usually have an AUX post but I don't know what they used it for. A lot of the later ones have a connect for a hall effect magnetic pick-up. Senders were more widely utilized after electronic ignition became more prevalent. I don't know what the numbers are other than part number or date code or something like that. SW used to have model numbers that had a coded meaning but that was back in the 50s & 60s. I don't know about later stuff.
This is a link to a picture of one over on the HAMB. I assume it is the same as the 8000 rpm unit. The 12 64 may in fact be a date code.
http://www.jalopyjournal.com/forum/s...d.php?t=604233