While it does go down to the month, I know that some have had difficulty registering vehicles without being able to "prove" (more than anything stamped on the vehicle) that it is indeed 25 years old. In the state of CO no less, so you should be aware that you're taking at least a little risk that you might have to wait a few months if you buy anything from 1991 right now.
....not that I would let that dissuade me, for the right truck.
The only reason I would consider an HJ75 with a 2H if I were you would because it would be an easy truck to convert to a 12HT.
The 2H will be difficult to start in the winter for you. Cold temperatures and high altitudes both make starting diesel engine harder, and the indirect injection on the 2H (and other engines of the era--like the 3B) will be smoky, and always a *little* iffy to start on cold mountain mornings.
The 1HZ is better at starting than the 2H, but still IDI.
Either way, you need to plan on a turbo. Especially living at altitude, without a turbo you're barely driving half a truck, IMHO.
An HJ75 provides an easy path to a 12HT powered troopy.
An HZJ75 provides an easy path to a turbocharged 1HZ, or a 1HD-T powered troopy.
I can't speak to AUStoUS's survey/inspection, but I am aware of a truck that went through that process and had a catastrophic engine failure pretty much immediately once it arrived in the US. You've always got that risk, and my experience is that Australian vehicles are generally not real well maintained. Australia has slower speeds, doesn't freeze, and has insane prices on oils--all of which lead to maintenance practices that don't hold up so well once they come to the US. I personally look at Australian engines as 50/50. Maybe they are healthy, and maybe they aren't. You might get lucky, and you might have to rebuild or replace the engine anyway soon.
Anecdotally, our Australian Engines are 50/50. One of them (3B) failed after about 10,000 miles (we then rebuilt it), and the other one (12HT) has been great from day 1.
Dan