Tires Tires,
I too am staying with the 13" wheels on my 1964 Dart V8. It is very frustrating to find the right size tires for this car but after many days of searching and finding dead ends I finally found the tires that are as correct as you can find and aren't trailer tires.
The challenge is not what is an equivalent tire size from a conversion chart but rather what tires are still made and sold right now! That is the challenge.
There were two sizes originally for these early A bodies:
6.50-13 (23.4" dia.) for 6 cylinder cars
7.00-13 (24.7" dia.) for V8 cars
The 3 sizes you can still find are:
185/70-13 (23.2" dia.) Closest to 6.50-13
175/80-13 (24" dia.) In-between 6.50 and 7.00-13
185/80-13 (24.7" dia.) Same as 7.00-13
My choice was between 175/80 and 185/80 for my v8 car (and these sizes are white walls!).
175/80-13 is $300/set
185/80-13 is $790/set
I went with the 175/80-13 at $300/set since the size splits the difference between 6.50-13 and 7.00-13 (sort of 6.75-13).
I just couldn't justify $790/set for only a little size difference.
Here are those tires compared to 1964 ad: