I used to have a very similar unit that I built to take advantage of the winch I already had in the bed of a truck. Later, I re-mounted the same A-frame to other trucks for hoisting engines or other heavy loads with a hand winch.
My observations:
1. This will work very well as a simple hoist, providing you don't expect tow-truck capacities with it. Yours looks better made than the one I used, and we never used anything like those tow-bars for attachement. Instead, we used the pivot points for the tailgate on the truck. It only took 5 minutes to put it on.
2. When mounted to a dump bed, the hydraulics make a very nice assist for a chain hoist. Pretty good for pulling engines or truck beds.
3. If you plan on running a winch line over that pulley from the bed of the truck, BE AWARE THAT IT IS CRITICALLY UNSAFE UNLESS THE A-FRAME IS CHAINED DOWN, in addition to being chained UP. This all somewhat depends on where the winch is mounted, and how high the A-frame is raised during use. If the load shifts or rocks so that the A-frame is more perpendicular to gravity than 45°, then the load pulling down on the winch line will have more forward force than downward force, and the A-frame will flip UP, dropping the load.
Don't doubt me on this, We dropped a 366 truck engine on the ground when we moved the "tow truck". I had it all on video, too. (Long since lost, so don't ask me to post it)