Right, mix the chilis as you prefer.
Paul-- Imo, its worth getting several chilies then trying them to see their qualities.
In the original recipe, 8 T of ground chilis are used (4 paprika, 3 chili powder*, 1 cayenne) so, were I to keep the same quantity (not really necessary), I might go with, say, 2 T each of guajillo, ancho, Aleppo, and cascabel or pasilla--or maybe just, say, 4 guajillo, 3 cascabel, 1 Aleppo.
Lots of possibilities. Much depends on the depth and type of chilie you want, and how much heat. Having several chilis at hand, and having some familiarity with each chile's qualities, makes this easy--and enjoyable--to do.
* chili powder is a blend of ground chile, often ancho, plus usually onion, garlic, s bit of cumin and/or oregano, sometimes sugar; the onion, garlic and cumin could easily be added to the rub mix if converting the paprika, chili powder and cayenne to more flavorfu chilis; I'd skip the oregano and go with sage and/or thyme though