55.2-59 18" wheels on 55 2nd series backspacing

[MALIBLOC]

On the new truck I opt'd for 18" rims to modernize it just a bit. I went with American Racing 18x8 and 18x9.5, the front are a 4.5bs and the rears are a 5.25 backspacing for meat I put a 235 45 r 18 and the rear I put a 255 45 r18.
IMO you may not be able to fit a 275 without modifying your fenders or bed side, the axle I had is a 6 lug that I had drilled out to a 5x4.75 so Im not sure if it was original to truck but I added a disc brake setup in the rear and drilled those out too, they added 1/4" to track width.
This combo fits perfectly on these truck here's some measurement pictures if this helps any.
Also if you every need tires order them thru Walmart and have them delivered to the store, their very competitive in price and offer free shipping plus they only charge $15 to mount and balance.
I have about 3/4" clearance on both sides.