Despite funny business in the OP, (90K tires! I want those!) (Two tires from the future! I want those too), I'll assume some minor mistakes were made and throw out my two cents.
Michelin RV tires, some of their brands, start cracking in the sidewalls very early especially in the sun. So what I'd do is take the offer, and put them on the fronts so I could monitor their condition and replace them quickly, in case. Then I'd always remember to put tire covers on them when I'm parked so they'd not see too much sun.
Good luck, CBone.