All A-body leaf spring assemblies are the same length and width. Typically the standard leaf for the A-body had 4½ leafs while the heavy duty units had 5½. I researched the 72 model year and turned up 6 different part number listings. The 4-doors used a different part number than the 2-door cars, which I found interesting. Rates are going to vary from year to year depending on what market segment was being targeted.
The mounting to the uni-body is going to be the same for all springs. The 7¼ axle had smaller axle tubes so U-bolts and shock mount are going to be drilled for a 2.75" axle tube. The 8.25 and 8.75 axles both had 3" tubes, so U-bolts and shock mounts will interchange.