You are correct, there are several versions of the Spiratone Dupliscopes. Maybe someone has put together a list. Some had the scale that you mentioned, but I think they were designed for the manual strobes that Spiratone sold -- although they could work with any strobe of the same GNs.
Your idea of a TTL set-up should work fine, but of course, you need a camera with TTL flash ability and a flash with TTL flash ability. One thing to keep in mind is that some (most?) TTL cameras and flashes will not work OFF-camera. For example, many (not all) Minolta Maxxum and Sony TTL film and digital cameras and flashes have a contact on the flash shoe that turns off TTL capability WHEN the flash is removed from the camera. Sometimes you can overcome this obstacle by getting a different TTL OFF-camera cable. That's what I did.
You may or may not have this problem with your gear, but keep it in mind. And there are different types of TTL flash to complicate the matter even more.
