I'll let Bob respond, but doing the math it sounds like the original axle gearbox is about 15.5-to-1. Then, 12/14 pulleys give you 18:1 and 10/18 pulleys give you 27.5:1. From what I recall, the chassis has to be "hogged" a little to make room for the large 18-tooth lower pulley. Also, the motor might have to be slid lower on its mount to make the belt reach without putting tension on the bearings.
When I heard Bob's idea I did this mod to my Greenbrier, that's how I know ;-)
