How universal is the 7-1/4" axle

There is NOTHING wrong with a 7.25 if you use it within its intended range. If your car is a Daily Driver/ Cruiser then the 7.25 is actually a better choice than the larger, heavier rear axles. This is why they were designed and built to begin with! There were no major warrantee issues or recalls, or redesigns in 13 years of production. It IS a fine rear as long as you don't ask it to do what it was never intended to do.
As for the original question, the 7.25 A Body axles are all completely interchangeable right up until 1973 when they went to the larger bearing and 5 bolt backing plate.
If you need 7.25 parts, PM me and I'll do what I can to get you hooked up.