I hadn't thought about the unfamiliarity of the "square" reference. Thanks for pointing that out.

There are a couple of obstacles to doing this type of set up on a vintage car and most center around the front wheel well. Tire width, height, and wheel offset are the three biggies. The maximum front wheel offset that can be used on a vintage Mopar using a 15" rim is 4.75". Any more and it WILL be hitting the ball joint. This limit in offset means you cannot use wheel offset to put a wider tire further into the well to avoid wheel opening interference. So now you are limited in how wide you can go in the front. This creates a self limited concern with the rear now as well. Additionally, since most vintage Mopars do not have round wheel openings to match the radius of a tire, the height can cause a concern with well lip interference, or if the vehicle is significantly lowered, bracing inside the fender. We also again have the front/rear match up look; a 26" tire that works good in the front may look short in the rear. Of course, you can section and bulge or flare a front fender to create additional space to allow a matching front to rear tire set up.

Of course this will vary from vehicle to vehicle and some will be easier to do than others.

My Challenger runs 26x10x15 front and 26x12x15 rear tires. They fit everywhere and only required two mods; offset leafs in the rear and rolled lips on the front. For grins, I did check out the 26x12 on the front. Ain't happening in a 15" rim without significant fender mods.