Big, heavy parts (of which a Unimog has many) have been the issue for me personally. I got lucky and found rims, tires, and a fuel tank in my state used, so shipping costs were not too bad. But I still spent $5k on rims and tires and the tires were NOS. Other parts I cannot find in the US like side steps, battery box, fuel tank brackets, and rear mud guards. Shipping those big items currently from anywhere overseas is cost prohibitive (for me). Actually, the fuel tank brackets I did find in the US, but shipping, even in the US, will double the cost of the parts. So I wait...
And then there are big, heavy parts that are aftermarket like some cool stuff Atkinson Vos makes. The only place to get them is from the UK. Stuff like sound proofing kit, fast axles, and larger fuel tanks. The shipping is insane. I recently priced fast axles with the recommended bearings and spacers with shipping and it was close to $10k USD. The sound proofing kit is I think £725 but the shipping was an extra £890 with a 30-40 day time.
Maybe shipping things will get more reasonable after the pandemic dies down? At this point I am thinking it would probably be a lot cheaper just to RORO the whole truck over to Europe, outfit there, and start traveling when done.
I am not complaining, just food for thought before you buy.