I used light munich and it turned out great. Caramunich would likely work just fine. It's a half pound, it'll be close enough.
Columbus would be fine for the bittering addition, I think Columbus works well as a bittering hop for almost all styles. I used Galaxy for the flavor/aroma additions in my last batch of this and while good, it wasn't as amazing as the Centennial was. Good luck with your brew! This is one of my favorite "as-is" recipes and really doesn't need improving on.
music to my ears!!! thanks so much.