For mud, that should be a decent ride. Locked rear-end, as you said, and some good tires would help. You said pulley, so I'm guessing it is getting speed up some. Wouldn't speed it up a bunch, that is a top-heavy tractor, and would flip easy. On the transmission, I'd install some grease zerks on the axles, just drill/tap the housing where the axle goes through. Then you can pump grease until you get some out the bearings on the ends. Front wheels should already have zerks. Transmission is a gear oil filled unit, so change the oil and it should be good. I'd put a gas pedal on for ease of driving.