To close this out, Andrew Meislin was kind enough to point me to Michael Breeding's website (https://www.mikesindianparts.com).  Michael provided the following:

Your Scout most likely came with the round 100185 Airhorn. Your M7 carb most likely came with the Linkert Airhorn-L.  Both will work. You choose the one you like. All Linkerts have the same mounting flange spacing, like your M7. All of the Scheblers I’ve measured have that same Linkert spacing.