what size tires for cat 212 grader?

The specifications I have show 10.00 - 24 for the rear tandem.

The 10.00 x 24's were correct at the time the grader was manufactured (1953), but this size became officially obsolete in the mid-1950's as tire manufacturers standardized on a lesser number of sizes.

If you acquire some later parts books, and compare the individual wheel hub/rim part numbers and drawings .. you'll find that either the rim pressing or the wheel hubs were modified in design, when Cat changed over to the 13.00 x 24 tire size.

From late 1955 to mid-1956, Cat changed over to tubeless tires on all motor graders, wheel tractors, scrapers and wagons. The new tubeless tires required a new three-piece rim with an o-ring seal.
Earlier model graders, wheel tractors, scrapers and wagons could be retro-fitted with the new tubeless tires, but the new tubeless rims were required as part of the deal.

You will likely find that the newer rims or hubs have a bigger offset to compensate for the wider tires. The changeover to tubeless tires on the 9T series motor grader came in at S/N 9T4762, in Dec 1955.