One of the biggest issues I see is the following: yes, you can have a whip butt loading arm, winch etc, but it takes something with a LOT of weight to anchor it down. The winch doesn't have to be very big even. But you need to start thinking about outriggers etc if it starts getting crazy.
One of my ideas for a winch was a Cub Cadet lawn lawnmower. Install the frame minus tires and steering. These have a driveshaft to a hydrostat with a differential and a brake on each side. One of the sides of the hydrostat would have just a brake and drive nothing, the other would be attached to a chain reduction drive to the winch drum. When the "drive" brake is on, the power will go to the reduction drive through the differential. The cable can be locked in by engaging the brake on the reduction drive side. Otherwise, with the opposite brake engaged, the hydrostat can power in and power out the cable or both brakes off to freewheel the cable. I have no idea how much reduction would be needed to make the winch power useable for skidding at what point i is just cheaper to buy a winch and add batteries.
The other side of the engine crankshaft (deck belt drive side) will power your pump. 20hp or so would run around 8 gpm single stage pretty well at high pressures.
you'd need at least 3 function control valve, boom up down, stick in and out, and boom rotate. 4 and 5 function would be nice to run a power grapple or outrigger cylinders.