what are good tires for 64 dart slant 6

Are you looking for a matched set of 4?

Mastercraft 05807, 51$ each. Not sure if they'd fit on the front because of the height but they will for sure fit on the rear.

Next tires I could find start at 185$.

Personally, unless you are in love with your 13" wheels, I'd move up to a 15" and then the door is wide open in wheel and tire election.