The real question is......how much weight can you add to the front of a cub without breaking something at the pivot point, which in this case would be the rear axle...........
Probably the only person who truly knows this, and what you could do to modify/reinforce a cub to do this particular duty would be rick prentice...
Here is what I do know....
The rear rockshaft with my modified hydraulics will pick up somewhere around 500 lbs, at that point, the lines burst. The front of the tractor (with a single set of front weights) does not lift up.
Trying to pick up the back of an A (1800 lbs) does not work. It begins to , and then the cub stalls -- this, I believe is too much for the little cub pump, even with my big hydraulic cylinder......the front wheels do come off the ground with one set of weights...the axle does not snap.....at least not right away. (This was with repaired lines....) I may at some point replace my 2" cylinder with a larger diameter one, so I can do more stupid things that get me into more trouble.........
I think it would be possible to modify a cub for this duty, but for your own safety, and for that of the cub, it would have to be reinforced in some way....perhaps with a subframe that adds the counterbalance weight......
subframe extending from the implement mounts on the torque tube through the drawbar mounts right through to the rear mount for the bale spear. Weight added beneath the belly of the tractor, as well as the front wheels, for even distribution and balance, keeping your center of gravity low.......
and, of course, the hydraulic system, as is standard, will not do the job.....you would need to design a much heavier system.