About 60.5 inches.
The CJ5 narrow track axles are about 50" WMS to WMS. The CJ7 wide track axles are about 56".
Essentially correct. I don't recall where one would find a 58" axle - was that listed as "flange-flange" or "WMS-WMS?"
What's the difference? "Flange-flange" would be a bare housing width (remove the brake backing plates and axle shafts, and measure between the flanges on the ends of the tubes,) while "WMS-WMS" is "Wheel Mounting Surface to Wheel Mounting Surface," or a measurement between where the wheels sit with shafts and drums in place.
Considering the lug pattern, and adding the six inches or so for brakes, that would bring it up to 64" or so WMS-WMS, which suddenly starts sounding like a full-size truck axle (not a bad thing - there are plenty of people running full-width axles.)
NB: You'll either want to get custom shafts made to revert to 5 on 4-1/2" lugs (to match the front,) or find a front axle with a lug pattern that matches your rear (if you can get a BoM number off of the 44 you're looking at, we can figure out more or less what it came out of. The BoM should be stamped into a tube, near the centre section, on the side where the cover would go. Six digits, starting with "60" or "61." The six-digit number should suffice - the suffix after that merely tells us what gears and differential it had. Originally.) Or - worst option - carry two spare tyres and wheels.
Given the commonality of the 44, it would probably be easiest to get new shafts made and make a note of what the axle came out of, and what you did to make it work. (You
do keep a running project notebook on your rig, don't you? Why for not?)