tire size questions?

[yellowjeep]

What is the biggest tire i can fit with a 4" sl and a 3" bl assuming i cut away some of the rusty sheet metal and what will the rim backspacing need to be to fit the big meats?

Thanks

 

[Leper]

With much trimming....49"
with a little less trimming......42" Koldsimer runs 6" lift and 2"body on his 42" irocs