[dmsfrr]

I have a Dana 44-T under a '55 Bird, and two sets of leaf springs.

I tried to keep these measurements from being too rough but they were made under the car while it was sitting on the floor, an interesting challenge.
The center to center distance of the spring pads appears to be 42 & 1/8"
The distance between the inner surfaces of the outer axle housing flanges is 52.5"
The bottom of the spring perch pad is 1 & 3/8" below the underside of the axle housing tube.

The eye center to center distance of the new replacement leaf springs under the car is 48". I also have an old set of leaf springs (with a couple mis-matched leaves) that were on the car when I got it. Laying loose on the floor the eye to eye center distance on those is slightly over 46".
The springs under the car are holding its weight and flattened out a bit, measuring longer than the loose ones off the car.

The old leaf springs have 6 leaves, the replacement leaf springs have 5 each.