Oh boy.
A ‘67 7.25” may not be the same width as a ‘73 7.25. The BBP 7.25’s are not the same width as the earlier SBP 7.25’s.
The 57 1/8” measurement is the SBP 8 3/4 width, which definitely is NOT the same as any of the A-body 7.25’s.
Using a tape measure and going over the center hump will make your measurement longer than the actual width, potentially by a significant amount. None of the A-body 7.25’s are wider than a SBP 8 3/4, so the 57.2” measurement is totally inaccurate.
And as for “measuring 100 and getting 100 different measurements”, that has not been my experience. I’ve measured dozens of Mopar 8 3/4’s, and all them were less than 1/8” from the specs in that list I posted when measured correctly. Their width is somewhat critical to the function, and unlike body tolerances they were held pretty tight.
Your ‘73 could be either SBP or LBP, depending on whether or not it came with factory front disk brakes. In 1973 the disk brake cars went BBP, and all factory V8 cars got front disks in ‘73. A /6 car could be drum/drum, and those care remained SBP. So, just knowing that it’s a ‘73 with a 7.25” doesn’t confirm which bolt pattern it is.
You can definitely use an axle wider than the A-body 7.25” regardless of its type, but your clearance to the quarters also depends on your wheels backspacing. And if you’re going from SBP to BBP that could be changing!