Those wheels sure look like they'd be 20 inchers'!!
I would be quite sure they were original too. The guy you talked to may be right about his insurance.
Since they still make those 8:25/20 tires, some competent tire shop will still be able to mount them. Just check around your area for truck tire dealers.
There are previous threads about the 'split rim' thing so you might want to peruse them on here. There's nothing complicated about them but then, they're not for amateur tire changer's either.
Good luck finding a willing shop.
