I actually came across it when reading the 1898 book: Cocktails, How to Make them.
The recipe predates Harry Johnson's and it basically consists of equal parts Plymouth Gin and Dry Vermouth, no modifier or bitters.
Olive Garnish.
I personally find the anisette version to be by far the most interesting, as often the case with Harry Johnson's versions, however,it is interesting to see how the cocktail changed through the years.

I Personally find the 2:2:1 ratio to be the best. 1 being Campari.
However, to make this work and balance the sweetness of the vermouth you d really need a punchier bourboun, whit an higher ABV.