A difference of 1/2" on the circumference of the lining probably won't make a noticeable difference. If you're referring to in/out depth of the lining, that's critical, as would be diameter. 1-ton brakes are pretty scarce items, since the 3800 sort of straddles the fence between a pickup and a full-grown truck. Brake drums are just about impossible to find. It would always be possible to get the old shoes relined if you can find an oldtime brake shop with the equipment to rivet the new linings on or a baking oven to install bonded linings. I'd really prefer a riveted lining if possible.
Jerry

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