If it were me, I would slide a jack under the pig and raise it up. Give the right tire a spin and see if you have an open or suregrip. Opposite tire turns opposite way equals open, opposite tire turning the same direction equals suregrip. You can also check the gear ratio by doing that. It may not be exact science, but it will certainly put you in the ballpark of knowing what it is.
If, for some reason, it happens to be a suregrip and IF it had more desirable gears, it would put the center section alone in the 400 to 450 range, and the whole rear in the 700 range maybe a bit more depending if someone just has to have it, lol.