This was the plan.
Now here is the realization (before making it pretty so you can see it warts and all) but with new log end clamp.
Unlike a Hi-Lift jack on its own it stands up by itself quite well.
The unit breaks up into 3 bits for easier transport.
The Jack with nose/lifter adapter attached
The outrigger or base - long blue and brown thingo
The log end clamp - blue and black thingo
Blue stuff is 1.2" SHS
Brown is 1.6" angle
Black stuff is rounded corner 1.2" SHS
Here a close up of one of the outrigger feet.
The outrigger does not need to be very strong. As long as it is big enough, very little side force is needed to hold the jack in a vertical position provided it loaded in a vertical position.
Here's the log hooks and top clamp.
The welding looks bit dodgy but I'm confident it will hold
The hooks can rotate and open wider to grab up a log end that is on the ground so no clearing under the log to get a grip on it. The hook ends are double gusseted 1/8" steel plate so should be very strong. The top clamp position is movable vertically and unless the hooks are spread this is about the closest grip that can be created without packing.
The hooks can also be moved relative to the jack for extra lift/height.