If a CUCV was pulling one, then either it was heavily modified, or an idiot.
I have an M720 over in my back field I bought from one of the other guys around here.
It's certainly heavy enough on it's own. I helped recover a shelter with another one, and it took 3-4 people to maneuver each half to get them attached.
The M720 itself has markings and rating up to I think 10 or 12k or more lbs, even though the Army only rates it for about 6k I believe. I don't think any of the CUCV series is rated to tow that much weight, even without the air brake issue.
The front and rear dollies are separate brake systems, so if doing an electric over hydraulic conversion would require 2 controllers.
I never found anything for converting the brakes over to electric, and after taking one apart it looks like you'd have to have new spindles welded on, so another expensive route to take.
If I were to do one to tow behind a larger truck, and everything else being the same, I'd probably opt for the M832. It uses the same tires as the deuce from what I've read, plus being a little larger/heavier built isn't a bad thing if you have a truck big enough to pull it.
M720 basically uses jeep size tires, a bit lighter duty