22-03 step 4 Countersink
I think the step you are referring to is pg 22-03 step 4. Mine was not a Q/B so I countersunk earlier. The part has a doubler behind so see no issues with the C/S. It fit up fine when assembled.
I would C/S and use the AN509 screw. Wouldn't want to take a chance on rubbing later when things wear a bit or after paint or some other minor change.
RV-10 40253 N253RV Flying
RV-14 140466 In build - Finishing kit
Douglas, GA. 2019 Dues paid