Maybe another way to skin the cat. Get one of the new 10 speed GRX rear derailleurs, a road link (just in case) and a Sunrace 11-40T cassette. New Cranks, GRX 2 x 10 gets you 46-30 Front. That should get you a granny close to what you need in BC, though last time I was there I was running a 20T chain ring and 34T rear.