The only way to have the 340 is with the A66 code package. Your car came with 15 inch wheels, 60 series tires, a collapsible spare, RT style hood, and a bumble bee stripe.
Plum Crazy with black interior. As far as the tires are concerned, I'm thinking 235/60/15 front, and either 275/60/15 or 255/60/15 rear. The reason for indecision is the height of the 275's is quite a bit higher than the 235's and I'm not sure that much of a difference is desirable. The 255's not so much of a difference in height, but also, of course narrower. Still looking for input to help me make this decision. I wonder what the pros and cons would be one way or the other.
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.
OK, so perhaps thats why so many people seem to go with the 275's in the rear. I appreciate that input. I think I'll go with the 235's front, and the 275's rear- both 60R / 15.