The last 4 sets of tires I've bought were all bought at our local Farm & Fleet. 3 times a year they run a special where you buy 3 tires with mounting and balancing, you get the 4th tire free. I'm always skeptical about these kinds of sales, but these guys have been legit every time.

Generally they will let you upsize the tires one size larger then the biggest tire available as a factory option. That works well for me, you could buy pretty big tires on a Dakota RT. I tell them the chassis under my 49 is a Dakota RT chassis. (it was a Dakota chassis under my 48 Plymouth coupe as well.)

They are very busy during the buy 3 get one free sales. You usually have to set an appointment (for about 2 weeks later), and the tires are waiting when you get there.