1974 Dart Frame Dimension Confusion

So I am checking my frame dimension to make sure I keep everything square when installing new quarters. This is on a 1974 Dart Sport.

I have the body service manual with dimensions in it. Problem is the dimension it has for the rear spring eye to eye of 57.26 isn't even close. Mine is more like 54.25 just eye balling it.

What's more if you look at the frame dimensions and use the 43 center to center and the 68.98 and use common sense right triangle math that tells us the the other dimension is 54.72, not 57.26 like the book says. So is the diagram wrong, and if so can I trust the rest of it?

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