Recipes specifically calling for Old Monk are so few and far between, I had to give this one a spin. The full ounce of Punt e Mes beats back most of the rye nuances and even most of the endearing harshness of the Old Monk. Certainly the Bénédictine comes through loud and clear. Successive sips do reveal more of the base spirits' character, but they definitely play a backseat to the Punt e Mes and Bénédictine.
I might need to revisit this one with good old Noily Prat to try to strike a rum/rye/vermouth balance that is more to my liking, but this is one that is worth further reflection and experimentation.
When we had it at Drink in 2008, it was 1 dash Mole Bitters. The cinnamon note of the Fee's would be delightful, but it was not the house recipe (the version of the Drink recipe book I have lists it as 2 dashes Mole Bitters and served in a rocks glass without ice).