How thick is the lining on the rear brakes?
Do they normally have brass woven into the brake material? Are the rivets normally even with the surface of the shoes?
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They are about 1/4" thick, normally hollow rivets used by countersinking the head in the material.
The brass split rivet install on yours will likely work a long time.
The shoe lining with brass wires is good against the steel drum of the '26-'27 emergency brake.
Indeed 3/16", I bought a set of '26/'27 shoes with new 1/4" thick lining - and learned why they probably were for sale in the first place.. No chance getting them in place without thinning the lining on a belt sander - and not very fun doing that considering it could be old asbestos lining. The lining has to be about 3/16" to fit in the standard setup. If you buy new repro brake shoes you'll probably have even more troubles, they're known to fit badly and has to be reworked.