Lena Phares

I have a 2018 3500 GMC Denali current tires: 235/80R17 tires to be installed: 285/70R17 (I already have them ) What spacer and where do I order the correct spacer for this to work? My tire shop only carries EZ ½” spacers, so they told me to research the one I’m going to need and order it for them to install since theirs won’t work and they don’t carry anything else. I haul a lot. I pull a 34’ gooseneck 4 horse with living quarters. I will be having it leveled at the same time as tire install. I just want my working truck to be able to do it’s job a little dressed up. Can someone please give me some guidance? Be nice.