According to the Perth site, http://pmms.webace.com.au/reviews/vehicles/tamiya/tam35263.htm the new tires are held on with polycaps so some modification of the old Tamiya HMMWV suspension will be required. The old kit is the same base Italeri kit so any aftermarket tires made for the Italeri or Revell of Germany HMMWV will fit the old Tamiya kit as well.
As for size, they should be just fine. The old and new Goodyear tires on HMMWVs are a different dimension and the wheel wells are plenty big to handle minor variations in diameter.