whats the biggest tires that will fit with a spring over lift

[Hammer]

so do you think xzl's 1600 x 20 would be to big , what would the biggest you would go . but what would you have to do to be able to run xzl's 1600 x 20 on a m715

As a matter of fact, I DO have pictures of what they look like!
SOA, 2.5" body lift on the front.
Rockwell axles.