I have yet to try this with Cassis, but it works very well indeed with Chambord and with cherry brandy, and invites one to carry on experimenting. Campari really is a most extraordinary ingredient - up there with garlic and black truffles!
I also used WT 101. I fiddled with the quantities since I like very little campari. I used 0.5 oz of Cassis and 0.25 oz of campari and I enjoyed the result quite a bit.
Found this to be a bit boozy as formulated but truly enjoyed the accord between cassis and rye spice - certainly not something I would've ever thought to try.