7.00x16 is the most popular, but original Kelsey Hayes wheels are getting scares. It all boils down to how original you want your Willy's to be. Most you find these days are 15" wheels with radials installed for better road manners.
Willys specified Gross Vehicle Weight by what size tires were on the vehicle - kind of strange.
From the nameplate data for the '48 Truck, you can see that it could be either a three-quarter ton or full one-ton truck, depending on tire size.
Since I only put 6.50 x 16 tires on it, I have to be careful how many grandkids I load into it. I don't want to void the warranty - per the warning on the data plate!