Hello Rusty, attached I believe is the info you are looking for. The picture is of my 1970 Mach1 with the measurement I have taken C to C. I have installed a 1970 Trans Am racing sway bar which I purchased a long time ago but it is mounted in the original factoy bolt holes. I did this because my original sway bar has large bulgy corners and would hit the P275's I have installed on the 8" wide mag 500's. When you install the holes ensure you tack weld a reinforcing plate inside the frame rail like the factory original, I would even beef that up to at least 1/4" thick, as I needed to use longer 5/16" bolts to mount mine on the spacer tube use on that bar and it would have been nicer if the backing plate was thicker. Trust this helps.