It's not stupid, people used to go that route with DH, some still do. You'll need to get a spider adapter to work on them. For the cranks, I'd look at Deity Vendetta crankset or The Profile Racing MTB Crankset. With the Vendetta's you'd have to run a spider adapter. You'll also want a chain guide to run it if you are going 1x9. Depending on your budget I'd look into an E13 32 Special if you want to run a 32 tooth on the back.