I have cleared up the mystery regarding the initial before “Gossett” on those Regent Street stamps: it is definitely “C”. I found this very clear example on the south side of Fernwood Avenue a short distance west of the intersection of North Hayford.

C. Gossett must have been in business at least a little while, as I found a classified advertisement in the October 29, 1949, Lansing State Journal: “Building, repairs, concrete work, and basements sealed.” Unfortunately, nothing else is given besides the name and a phone number.