The Old Waldorf-Astoria Bar Book by Albert Stevens Crockett (1935, p.39)

2 dashesorange bitters base
0.67 partsloe gin base
0.33 partsweet vermouth — Italian vermouthmodifier
  1. Stir the orange bitters, Italian vermouth, sloe gin, and ice.
  2. Strain into a cocktail glass and serve.

See also: Black, Sloe Gin