The truck motor is common in the USA as well as reasonably common in Australia. Obviously Japan would have once had many but they seem to replace vehicles faster than any other nation!
The motor can come from a Land Rover or truck, the variant in the Perentie is an industrial rather than automotive engine but the differences are few. Best bet is to get a 4BD1T from a truck if you want decent performance on the road. The later years are a little more refined than the earlier ones. My 110 CSW has a 1984 motor versus the 1994 motor in my Perentie, the Perentie is a touch smoother and quieter.
Gearboxes used in 110s behind the 4BD1 are both the LT95 and the LT85+LT230. For the LT95 (unsure of LT85/LT230 combo), you need one with .996:1 high range, or the low-revving engine will be revving its tits off at highway speeds even with 33"+ tyres.
The bits between the engine and gearbox are the hardest part to find. The LT85 bellhousing in particular is fairly uncommon now. But all the parts do come up when you look hard enough or long enough.
There is/was a company or two in Aus making adapters to match an Isuzu 5 or 6 speed box to the LT230, which would be ideal really as even the robust LT95 suffers behind the 3.9l four pot, if laboured hard (and the engine loves to labour, bucketloads of low rpm torque...)
Outback, if you're properly stuck and still wish to import to the US, I can try and help you out, though I am slow as a wet week with that sort of thing, and am not a professional! Contact via PM on this forum (or isuzutoo-eh on AULRO) is best to start with.
I love my FFR