It will be OK. You will have to figure the rolling circumfrence to make sure you do not get "wrap up" if you are running 4WD. There are some good web sites to help you figure this out. Try Titan tire site.
If you use the factory R-4's and the factory Ag tires the ratio would be off.
You would have to run a taller front R-4 or a shorter Ag tire in the rear to get the ratio back.