Whoopee - another tire question...!

OK, I know what will fit, I can't decide what wheels I want, but I have one question:

Do the radial tire sizes listed in the Dodgestang chart, or the Halibrand chart (amongst others) have an overall diameter similar to the original 6.95 x 14 crossplies? If not, I assume they are smaller in diameter - what do you guys do about speedo readings?

We have so many speed cameras over here, and traffic cops with laser guns hiding behind trees, I can't afford to be not knowing how fast (and it WILL be fast) I'm going...

One speed camera, less than 1 mile from my house, rakes in over a million pounds (that's pushing 2 million bucks) every year in fines.