Tire sizes

Your 265 R70 16 would be your best bet for plowing. The 17" tire you would need new rims. They can go on there, usually the profile of the tire they would match up to the tire size that would go on the truck. So diameters of the tires would match original tire size. Then you speedometer would still be accurate. 235 in my opinion is too small for the truck.

I plow snow and 235's would not work well in my opinion. I run 285, 70/17's on my Ford F150 and they work well. Small tires will reduce your traction, load carrying capacity and ground clearance. I don't know where you are tire shopping but I find a good selection of new tires in your stock size as well as 255 and 265 tires. 17's have a great tire selection but don't raise your truck up too much as it will screw up your snow plow angles.