If my math is right the percent difference between 13 and 14" brakes is ~7%. Meaning that given same shoe width (and perhaps also assuming same area of friction material) the smaller drum is about 7% less effective. As you pointed out I too expect there is more to consider for a precise difference but still no doubt that larger diameter drum is better.

Again, to compare and figure if the brakes will interchange measure space from the hub where the drum meets it over to the flange on axle, this is a primary dimension as far as how the brakes fit. No other variables or assumptions playing into it.

•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-