Yep, I am missing some of the really exotic attachments. I would like to find one of the post hole diggers, the trencher attachment, and the front mounted 540 rpm PTO for the tube frames.
The G12 seems to be a but uncommon here as well. The G9 is another one that is seldom seen, along with the 1257 which was basically a 1256 with a Tecumseh engine instead of the Wisconsin that Bolens preferred to use in most of their tractors.
As for the G12, I think you may have something of a 'Frankenstein' tractor, as all information I've seen on it shows it as having the 6-spd transmission.
One of my G11's (the one with the snowblower on it) is setup the same way as your G12. The original owner had transmission problems with it, and after finding out from the dealer the cost of repairing it, decided to transplant and entire 1050 rear end.
That gives it the controlled differential, which it originally lacked, as well as 12 speeds. In 1st gear Lo/Lo and it just creeps along. I haven't tried to see how fast 3rd Hi/Hi is yet.
Here's a short video of it in 1st Lo/Hi and then in Lo/Lo :D
https://www.youtube.com/watch?v=a6xbaP1DH6E&list=UU1Uz61LmXc5LyoDSnOOsWBw