Be VERY careful with those tall-wheel walk-behinds. The drive wheels are a low-RPM, high-torque drive. Forward pulling force calculates to torque divided by wheel radius. That big engine, with high ratio gearing, will put a HUGE amount of torque on the axle.
Action equals reaction. Counteracting torque is transmitted to the operator's handlebars. If you are walking behind one of these machines when it hits an immovable object (stump) those handles are going DOWN. If they snag on your belt your pants are going down, too. It could be worse -- much worse -- if your anatomy gets involved. And note that the that you will have to take one hand off the handlebars to disengage the clutch.
Gravelys, with their squatty drive wheels, apply less torque to the drive axle. They are not quite as bad.
Suggestion. Buy two sets of snowmobile treads and turn it into a crawler, with the treads extending well to the rear, and the operator safely on top. You could still mount a stump grinder at the front.
That looks like a 50s vintage Wisconsin. Low RPM, lots of grunt. If you take care of it, it will serve your sons and their sons to the fourth generation.
Pat