Well in my opinion, the G25 would be compatible for 13/18 gears. When you reached 6th, you pressed a button to switch to the Hi range, and then 1st would become 7th/8th, 2nd would become 9th/10th, ect... (maybe I'm not numbering the gears right?) it wouldn't be hard, just a matter of making the same control for the 1st to become 7th when the button was pressed. Good luck on building the shifter by the way
