That would have been quite a trip, you must have gotten a lot of curious looks. Unusual vehicle and steering wheel on the wrong side to boot.
I have seen a couple of these trucks in person, seems like quite a few of them somehow made their way to Colorado and other parts of the Rockies. Interesting and cleverly engineered vehicles in all respects. One other feature of them to keep in mind that is different from the Volvo car versions of the engine, and that I just remembered relevant to your original question, is that the electrical system is the military style 24v, rather than regular automotive 12v. That means parts like the two solenoids on the injection pump are different for the higher voltage, and of course the alternator and starter, and maybe some sensors are different too.
You may want to search around for old posts on this forum by a member with username Hecklebone. He was also in Colorado and had a 6x6 P90 TD automatic truck that he did all kinds of work on, including engine modifications, upfitting of extra overlanding equipment to the truck, etc. He sadly passed away three or four years ago, but his posts are still here and you might find some useful info in them.
For parts, best bets are usually the main Euro parts supply houses like AutohausAZ and FCP Euro. They both have a lot of offerings for the D24T engines, but it can be challenging to find your way to them, sometimes by looking up a Volvo 740 TD but sometimes you also have to look under something like an '85 VW Jetta 1.6 TD if you want things like glow plugs, injector heatshields, etc, or under a common gasoline 5cyl Audi car if you are looking for certain engine gaskets.
RockAuto has some parts too, but watch out for them trying to sell you parts for the Volvo 2.3L gas 4-cylinder engine, which is completely unrelated and has no parts in common.
Their application listings are more sloppy. Some sites will even offer to sell you an ignition coil or set of spark plugs for your diesel engine, LOL.
Brickwerks in the UK is another good option for parts -- on there you can look it up as a Mk1 VW LT van which also used the D24T and D24.