Kelsey Hayes SBP disc brake questions

Ok, I brought a caliper in to "work" with me. I'm stumped. These bolts look good, apparently the length is good at 1.75". But they bottom out in the caliper with 3/4" of smooth shoulder sticking out of the one half. Now when I measure the unthreaded hole/boss, its 1/2". Now add a flat washer, that's another 1/8". Soooo
.75-(0.5+.125), leaves approx 1/8" "excess". So either the bosses have been ground on(unlikely) OR the threaded part of bolts(reproduction) is shy approx 1/8".
Ideas??
Thanks again.

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