My only concern with running 265's and spacers would be when you are hauling something and the rear end is squatting. That combo might push the tires out to the point of interference with the fender. As far as the safety of the 1/4" spacer, I am on the fence. Make sure you have plenty of thread engagement with the lug nuts, and be diligent about making sure they are tight, and I think you will be fine. Just slap them on there and call it good, and you might have problems.
How much room do you have between your current 235's? Namely at the bottom where the tires bulge out.
I'm thinking maybe a set of 265/75-16s on the front and then 235/75-16s on the duallys should work ok. I'd like more tire, but I think I'd run into more problems than its worth. This way the tires are the same height, but I can get a bit more meat up front, instead of running the skinny dually tires all around.
Just a heads up, in this post the 265/75 and 235/75 sizes are NOT the same diameter.
265/75 and 235/
85 are the same diameter, however.
This may have been a mis-post on your part, but I thought I might make that clear for anyone else reading this.