I'm inclined to say the "480" you're looking at is a unit number, possibly from a rental facility or something. The Beaver III is an S373 by Satoh, parts and manuals are available from Valley Power and some others. The tires are mismatched, obviously; you'll be wise to make sure they're the correct size for the drive ratio.
The maintenance parts for my Japanese market equivalent were simple to find, though I don't recall offhand what filters they took. A search here will reveal the correct part numbers. Napa had them in stock, and the fan belt was simply matched by size.
I run 5W-40 synthetic motor oil in everything I own, from pickups, ATVs and dirtbikes to tractors, ski boats and crotch rockets, but any 15W-40 diesel oil is fine too. The hydraulic fluid will be universal tractor fluid, something that meets John Deere 303, IH Hy-tran, or equivalent will be correct. It is hard to tell, but the loader may have a separate reservoir and pump; make sure to check that fluid as well, and change it if you do the rest, too. The front axle will take gear oil. A service manual will tell you exactly what, but I got a deal on a case of 85W-90 synthetic, so run that in my machines.
Any high quality coolant should work at 50/50 ratio, (I use whatever is on sale, and dilute it to 50/50 with distilled water) but I like to run a little surfactant (Water-wetter or equivalent) and do a flush of the system first, just to be safe.
