Need help assessing this 1965 Dodge Dart 270 4-dr sedan

If you're not worried about keeping it stock, I'd consider doing a big bolt pattern disc brake conversion and get some 15" wheels for it. I just had a 225/70/14 tire go bad and had to order it. Just had to wait a day, but 14" tires are getting phased out too it seems. If you're going to keep the stock 13" wheels, take a look on the Discount Tire website.
I think I'd like to keep it stock for now. How can I find out what the original tire size was? Thanks.