I have read several of the messages on this topic and am confused. I need tires for my '54 3100. The existing tires are P215 75 R15. this would lead me to believe that I have 15 inch rims. (The rims measure 16 + from outside to outside.) Is this stock or were the rims changed somewhere along the way? My owner's manual says the tires should be 6.00-16-6 This would appear to need a 16 inch rim however I am not familiar with the rest of the designation. What size rim was provided stock on the truck? Would it be OK to put a larger diameter tire on the existing rims? Thanks