The spring perch measurement is for a B-body but the backing plate measurement is about right for and A-body. The 3rd member housing number is for a '57-60 model car so it was probably pieced together. What is the bolt pattern for the wheels? Maybe aftermarket ones? Be carefull it's not an early housing that uses the tapered axles. Those need a puller for the hub and drum assy's and are not the best design. You can use this housing in an A-body by moving the spring perches in an inch but check overall width for tire clearence.
Thanks, Mark
