I finally had a chance to get my 255's mounted today.
I had a little bit of rub on the front inner fender liner so I went directly home after the tire shop and heated, pushed, and re-drilled the inner liner as well as trim just a bit off the front bumper. Plenty of clearance there now. They are close to the cab mount but so far have not contacted it. I'll probably chop that down the road for good measure. The only place I seem to rub now is actually with the back tires when it is really flexed and they stuff in the wheel well. Luckily, it's a very minor rub that will probably go away by the time the tires are half worn.
I was also able to stuff a 255 in the factory location by cutting off a tab above the track bar that is used to center the OEM size spare. Unfortunately, this tab doesn't allow a 255 to sit up into the spare tire well and lets it hit the track bar. This tab also keeps the tire off the charcoal canister so in it's place but a little higher up, I welded a piece of 2" x 3/16" flat strap to keep the tire off the charcoal canister as well.
It's very close but it clears the track bar by about 3/8". In order for the 255 to sit up in the spare tire well, I had to let all the air out, get it into place, then refill the tire. It's a very tight fit and what I would consider the largest tire that could possibly fit there. A half worn 255 would probably fit no problem so I may do a 5 tire rotation until I reach that point.
The long term plan is to purchase or build a high clearance rear bumper with a swing-out tire mount. Hopefully, the OEM tire hoist is strong enough to hold this 255 up there for now.
As for the tires themselves, I like them so far. They're not as quiet as the KO2's but they are quieter than the KO's on my 5th gen. I wouldn't be surprised if these do get loud over time though. I have 40 psi in them and there is barely any sidewall bulge which leads me to think I could probably run them at 35 psi and be OK. For a Load Range tire these Coopers ride amazingly smooth, maybe even smoother than the KO2's. They handled the little bit of dirt and sand today with ease. I haven't driven on them enough to determine if these pull like some say they do or if the tire shop did an OK job on balancing. So far I'm a happy camper.