Chrome was original, but all but the really knowledgable won't know or care about the difference, and it isn't that noticable. Chrome bumpers were available as an extra-cost item on standard trim, but came standard with the Deluxe package. The rear bumper might have been an option, I can't remember for '54.
The mirror should have locating spots inside the cowl to start the drill bit. I think there is a tech tip on this here or at chevytrucks.org.
