This is an intek 18.5 HP hydrostatic tractor with a PEERLESS TRANSAXLE - 2000-006A and a blown head gasket. My guess is that after the gasket blew the tractor sat outside and the freewheel lever rusted in. The rear wheels would not both turn in the same direction. When pulled it skidded the wheels.
The net talked about the freewheel problem but I did not find any images.
Here is my take on the problem.
The freewheel control rod has a spring (in blue circle) between it and a lever on the transmission. The rod will always move but it can just be stretching the spring instead of moving the lever that pivots at the arrow.
You may be able to tell what is going without pulling the seat pan off the tractor.
If your rod sticks out like this when the rod is not hooked (set so the engine should drive the tractor) the lever is stuck in the position for pushing the tractor. If it not stuck too hard pushing the rod in might move the lever into the 'engine drive' position.
I soaked it down with penetrating oil overnight and tapped the lever back and forth till it was free. That took a while so don't give up and keep using the oil