Tires for 1968 GMC Handi-Van.

I think I'm going to keep my stock GMC 14" wheels and have them powder coated. Therefore, I'm hoping to stick with the stock 215/75R-14 tire, but I know that I could go with a 205/75R-14 or 215/75R-14....would changing the tire size affect how the van drives much? The stock 215/75R-14 tires are hard to find, but there are several "trailer tires" that are 6-ply and rated for highway use. Any feedback on the tires / wheels issue is appreciated!

-Nabor J

Someone told me I should go with a 6-ply tire on such a heavy vehicle, especially since I will occasionally use it go on dirt roads here in Oregon. Four 6-ply tires will cost $520.00 mounted and balanced and 4-ply tires will cost $320.00. What is everyone else running tire-wise?

Had 205/75/14's all the way around and was a nice ride, but got me some cheap and fake Cragars that have 275/50/14's on them now, and love cruisin on those for the time being , although steering is harder now, but i'm young enough to deal with it!!!