Original reference is dead. Internet archive gives the same ratios, though I wonder if that is because they want to sell more dry curacao? Internet recipes vary wildly, but that's the most curacao in any of them & makes for a big drink. Since this was attributed to Regan, I looked in his book. He calls for only 1/2 oz of curacao. He was not the originator of the drink, though, writing "I enjoy the combination of brandy and port, so this recipe from the 1950s caught my eye. It's a little too sweet without the bitters-I recommend at least three dashes. Orange bitters can also be successfully used in the drink." (no idea if that last remark was just to sell more bitters (ha!)).
My bad, I didn't read the earlier posts closely enough.
Interestingly the MixologyTech "Cocktails from the Golden Age" app has a "Betty Ross" cocktail from Sloppy Joe's Cocktail Manual (1932), with a build of 1 oz cognac, 1 oz port (ruby or tawny), 2-3 drops of curacao & 2-3 drops of Angostura bitters, which would seem to predate the Gaige's. Not sure how much you'd notice 2-3 drops of curacao in a drink, but this would certainly appear to be drier than using equal parts curacao, even with the reduction in bitters.
Well well... excuse me while I break into some Peg + Cat (you've gotta have a 3 year old to get this): "Problem solved, the problem is solved, we solved the problem, everything is awesome, problem solved!". So... EUVS has the 1932 Sloppy Joe's cocktail book and it's got the "Betty (sic) Ross" cocktail which is indeed cognac, port, and drops of curacao and Angostura. My guess is that liqueurs were much sweeter (closer to max soluble sugar) and more intense than they are today, so drops of curacao would work. I will update the link and the recipe. Thanks, Zachary
While I'm familiar with some of the historical cocktail literature, I'm far from an expert, but I do wonder if the "drops" used in the Sloppy Joe's Cocktail Manual are more analogous to a current (or even historical) "dash" or "dashes" and not what we currently consider drops (typically using an eye dropper). Pretty much every recipe in that book you linked uses "drops" measurements for everything from Ango to grenadine to creme de menthe, with no dashes, which you simply don't see from cocktail books from the same era. For instance, look at the recipe for the Mary Pickford. Sloppy Joe's has drops of grenadine & maraschino, while others from a similar time frame typically use 2-3 dashes (Libro de Cocktail, 1929) or bar spoons (Manual del Cantinero, 1924) for those same ingredients.