Tincup's 63 Dart w/5.7 Hemi

Ryan, It's no problem at all. I am by no means an expert, all I can really comment on is what I have done. The best way to measure for the axle is to place the wheels and tires up under the car where they are going to be then measure. My rear measured 48" flange to flange, overall 53.5" with a pinion offset of 0.75". The spring perches are 36" however I would only get them tacked in position because you have to set the pinion angle (typically 3 degrees).
Are you minitubbing or full tubbing? if mini I would recommend your axle be at least 1.6" wider than mine, ( my backspace is 6") my tires are slightly closer to the frame than to the outer wheelhouse. (I'm considering a 1/4" spacer just to center the tire in the wheelwell a little better). I think it is better to error on the short side rather than long. It is easy to add a little, but a ***** to take away. If I were you I would go with a 55.5" overall dimension, but please double check all your measurements.
Hope this helps.

My measurement was done with the wheels under the car and centered as best as I possibly could.. I have noticed with these wells that it would be better to have them further in then out because of how much the outer wheelhouse leans in and the inner goes practically straight up. The car is mini-tubbed, not full tubbed. Having them further in means they can always be spaced out as well, although I would really prefer to just do it right and not have to space the wheels. I'll be going with Bill's rear suspension setup so pinion angle will be adjusted through the upper links, not the pads. Your spring perch measurement matches mine which is good! Can you list your wheel and tire specs for me(offset & backspacing)?

Here are some pictures of how the wheels are centered when I took the 54.75" measurement. As well as just a couple other pictures of the car.. the stance isn't right in the front or rear, so ignore that for now.

http://img19.imageshack.us/gal.php?g=dsc01365la.jpg