An excellent drink! I've been making this with Rye instead of bourbon - Jim Beam's of late. I also tried a variation using Jim Beam, Amaro Nonino, and (instead of Aperol) an aperitivo I found in Paris when I was (unsuccessfully) looking for a bottle of Select- Poli's "Airone Rosso." It worked very well. (The Italian shopkeeper in Paris told me that Airone Rosso is very similar to Select.) I also sometimes add 1/8 to 1/4 oz Luxardo maraschino liqueur. And I sometimes substitute Ramazotti for the Nonino. There you have it.
Had to sub Meletti, and I drink Rye not Bourbon, still loved it. Looking forward to playing around, maybe trying Cardamaro or Grand Poppy next time. Campari would be too overpowering imo especially if using a stronger flavoured Amaro in place of the Nonino. Lots of opportunity to experiment with this one.