The gun likely started life with original Parker Bros. SST, see the R and L on the trigger plate --
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and was later converted to a Miller hence the R seen on the top tang.
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The gun is from about 1922 vintage originally, five years before Senator John was born. The beavertail is the shape shown in my repro April 1923 and January 1927 catalogs. The vent rib isn't yet included in the 1923 catalog, but is in the 1927 catalog.