Transmission looks like an old 3-speed car, say 34 thru 38 or so. They drive it from the rear and the roller is driven from the front!-- don't know why that is. It probably would work o.k., but owner never finished it up so this whole thing might be questionable!
One idea I have is to go with hydro-drive. 10 or more hp engine running a fair sized pump and valve for go-woa-reverse. steering could be hydraulic cylinder. the gear box in the pix. might be too slow response in small areas.
Just thinking out loud here! Comments welcome!

"A machine you build yourself is a vote for a different way of life. There are things you have to earn with your hands."