I bet they're common on a lot of 3/4 and 1 ton Fords back in the 60's and likely earlier and later.
The reason they seem a better fit is the 14 bolt axle tubes are not the common 3", 3.5" or even 4" like a lot of other axles are (I forget exact diameter, need to measure again). Though close in size the original GM saddles wrap around a fair amount of the circumference and won't fit the 14 bolt tube
The Ford version on the other hand does not contact much of the axle tube and while still not the exact same diameter as the 14 bolt tube it can easily be adjusted to fit.
Both the original AD GM and the 60's ford saddles shown in the background of this PICTURE

By the time the 14 bolt came out they used leaf springs wider than 2", so saddles for the axle won't fit our old springs.

Last edited by Grigg; 01/20/2016 3:18 PM. Reason: add picture
•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-