Just curious; why do you think you need r1's?
what you are proposing sounds like a very expensive proposition
you will have to properly match the fronts and rears (to prevent undo drivetrain strain), so you probably have to buy all 4 new wheels/tires
my DK90 has exactly the same wheels as kubota's wheels. They are chinese-made. I think tons of modern tractors use the same ones. I also think their are different grades from the same supplier, as I've seen similar, but less beefy wheels than mine on other tractors.