There's a good chance you'll need the pinch-weld-mod
with a 9" wide rim. If the backspacing is 5.75" or the stock 5.5" you might
be o.k., but most of the 9" rims have a 4.5" backspacing.
Since there are a limited selection of tires in this size, approved for a 9" width rim, I'd either use your stock rims, or find an aftermarket 8" or 8.5" width rim, if you are set on this tire size.
Nitto TG states 8.5" max. rim width.
BFG AT KO doesn't list a 275/70/18.
Toyo AT also state 8.5" max. width.
Goodyear Wrangler SilentArmor has a 9" max. rim width listed at Tirerack.com for this size.