When served straight-up, the Monte Carlo fits into the Scaffa family of cocktails, but it's much better and more usually served on-the-rocks, so best described...
Many thanks, Lynette. I'll add a Kentucky Colonel and Monte Carlos to Difford's Guide as soon as we've been able to photograph. In the meantime, I've added notes under variation. Do you know the names of any of the other variations based on other spirits?