Hello all - have a 68 Firebird coupe project that has had both front to back floor halves replaced, front leaf spring mount plates, and back halves of both rear rails sectioned in. In getting ready to put my new leaf springs in with the rear end, I dropped some plumb-bobs from the rear rails to check some measurements. My side to side measurements on the rear rail front mount gauge holes are on, my rear side to side from center of rail leaf spring mount hole are on, the front to back measurements on each rear rail from the front mount gauge hole to the center of the leaf spring mount holes are on, BUT my cross measurements are not!!!! Left side is 1/2" longer than the right side. Measuring from the right front to the left rear shows 1/2" longer than the same cross measurement on the other side. If those other measurements are within spec, how can that cross measurement be off???? I am puzzled by this. How can this be? What issues am I facing now with any rear end alignment or spring binding? I am no expert, just applying what I have learned while working on this car!