I have no input really on your tires, I think its personal preference. If it were me I would try to match the size of the original tires that would have been on the car but I think it has a lot to do with what your plan is with the car. How do you plan to drive it? I'm more interested in the car itself, can you post up some pics? The A66 cars are my favorite of the '70 Challengers. They were the result of Dodge having to backpedal after finding out that the Cuda was available with a 340. Dodge had no intention of putting the 340 in the Challenger in 4 barrel form. They put the A66 package together rather quickly and it was only available on the JH cars but included everything that the JS cars had. They are unique in this way and are considerably more rare than Most of the R/T cars with only just over 7,000 including verts.