Pack it good, use the original factory box and add more packing, then put it in an outer box, no markings at all other than the shipping label. Bubble wrap everything to keep it from rubbing the finish, pack it so it can't move when it's rough handled, if you can shake it and there's movement inside, it's not packed good enough. Just an FYI, when I've ordered accessory barrels, I only shipped the frame in a small flat rate priority box, I usually ordered a stock set, so all they need is the frame, of course that wouldn't apply to most repairs, although one member sent just his frame in for a trigger job.
Tim