Chinook is one of those hops with a very strident presence as a bittering hop. It can come off as harsh. It's a wonderful hop and the alphas are right for bittering but it can lend a little too much lingering piney bite if overused. A brown ale can stand up to some strong bitterness and the flavor profile is a good match so it's a solid choice.
I'd get no more than 1/3 of total IBUs in the 60 minute addition using Chinook. Then come in with a good flavor addition at around 20 minutes giving equal IBUs in Chinook and Cascade. Then finish with a good dose of Cascade at the end, maybe 5 minutes, to round out the IBUs and pack in flavor and aroma.
You end up using up a little more hops with a schedule like that but staggering additions and utilizing the same hop at different times adds a lot of complexity.