You guys have got me going.
I have Bolens hydro lawn tractor with sick engine as well as spare set of rear wheels/rims.(for front)
Being as to how steering is not required a straight front shaft would mount the wheels and naturally tension devices would be needed.
For track support I'd use HDPE strips as sliders rather than idlers.
Also have a 16HP engine waiting for a new project.
To steer I'd resort to differential braking* and my tracks would be conveyor belting using T bar stock for grousers.
I'd be counting on rear tire to tracks friction rather than large sprockets.
*Disc brake exists on left side so I'd reproduce for rt side.
Another option would be GOcart hydraulic brakes on both sides.
My 'tractor' would not be to push, dig etc but merely to negotiate the steep rugged terrain and haul me and tools etc around.