Green’s Dictionary of Slang

1. a ‘masculine’ male homosexual.

1949		Monteleone Criminal Sl. (rev. edn) 153: mason A homosexual type who takes the active part.
1951		D.W. Cory Homosexual in America 112: Most of the words [in Amer. Dict. of Slang] were of infrequent usage: agfay, lavender boy, mason, nola, queervert.

2. a lesbian.

1972		B. Rodgers Queens’ Vernacular 70: any gay woman [...] mason (dated, hetero sl, ’40s, because she lays bricks = homely gals).
1982		Maledicta VI:1+2 (Summer/Winter) 133: Here are some obsolete or nearly obsolete terms which careless lexicographers continue to list as current […] mason.