1968 Plymouth Barracuda Fastback (old school build with a new school feel)

RustyRatRod said
You've got me curious. Why 56 5/8"? That's a good bit too long for an A body rear axle housing.

That is total width, wheel mounting surface to WMS, not just housing width. Which is narrower than the A-body 57 1/8" wide rear.
I went this length because it was what worked with the wheels that I wanted to use. Also for the axles I already had.