Yes, the Toyota axles are just like our rear axles, a one-piece housing. There's no "tube swapping" to be done, you have to very precisely cut the axle housing and re-weld it back together. It's not a simple task, and I don't think it would be at all cost-effective.
It's been done by the way: http://www.nissanoffroad.net/how_to/SAS/sas2.asp

For anything but one-off projects, I'd say just stick with the tried-and-true driver-drop D44 from a Wagoneer or old Bronco, much cheaper and therefore easier to market.
Calmini was rumbling about making a custom axle either from an H233B center or otherwise accepting the H233B third-member, with custom tubes/shafts and D44 outers/knuckles.

I've got a wild hair to eventually build a left-drop H233B from one or more Patrol axles one of these days. Plan is solid, not terribly complex (doesn't involve nearly the cutting/welding of the above Toyota axle), but may be pricey regardless.

Brent