Sorry for the noob question guys.
Anyway, I already "did" it last night. Thing is, I thought the crown guards were supposed to be interchangeable considering both reps were Luminor cases. Swapped the 390's for a 005's and a 366's and either the lever doesn't completely close or the crown guard won't screw down as flushed to the case as possible. Long story short, had to put everything back together again.