Instead of putting 6 295/80/22.5s on the rear of my 04 Dynasty (had already gone bigger on the front) I put Hankook 11R22.5 as they are the same diameter. With a tag axle I did not need the load carrying of a 295. I would not go with the much smaller diameter or a 70 series tire.
How much weight do you have on your rear axle?
This post is my opinion, worth what you paid for it.
Our New ride...08 HR Navigator 45. A nice upgrade after 14 years with a 04 Dynasty 42.