I've found a used whole old truck crane for about $7,500, its rears may be too light, and I have no idea on condition of the axles., Don't know the ratio, (probably low) but its from 1977, so they would need a whole rebuild. They aren't direct drive like mine- they are planetaries, which is most of what you see used. At least with the whole crane I would get rims (my rims are also unique), and a set of steer axles, which are also japanese (suspension isn't). And the axles are from 1977, even if they are rockwell, they may not have parts available.
I'm getting my truck parts man to price new, which may scare me to death. But if I have to buy the old crane for 7,500, spend another 5,000 getting it home, another 5-7,000 revamping and installing, 25,000 for new axles isn't that far away.
Yes, it is 10' wide probably 60,000 lb housings. I have searched the big salvage yards for used, but none around. I could live without the exact ratio I have now, but I would like to be close.
I don't think single drive will work either- its how I got home, but one little dip and a wheel in gravel and you've got 97,000lbs stuck, or spinning, and that's a good way to destroy axle shafts that are also unavailable.