215/75/16 is about the closest modern radial that you'll find to a 7.50-16. it will be a bit wider, but not much. If you're only going to get 2 tires, the radials must go on the rear, per DOT reglations as well as tire manufacturer suggestion. best bet it to wait until you have the scratch to do all 4 at the same time.
RAK, 31x10.50s should work fine on the front of your truck. I've put 32x11.50s on the front of a similar truck with no rubbing.
