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Continuing to research this upgrade, and found the brake shoe frame design chaned in '78. The size of the lining and drum stayed the same. However, '77 and older used a different brake shoe frame design, along with likely different internal parts too. The holes in the brake shoe frame are different between '77 and older, and '78 and up.
Still researching if their are differences in backing plates between '72 and Earlies 80s, along with C and K vehicles.

Jimmy, using K drums for 6 lugs.

L