Here are pics off my 66 k10:
First pic is taken from under the bed, pointing towards the front of the truck. Inside frame rail on passenger side. The hardline connector you see is almost lined up with the transfer case. Bracket for "transfer case to frame" can be seen in background.
Hard line seen in previous pic follows curves of inside frame til it meets at this point and connects to rear rubber brake line. Still on passenger's side of frame.
This shows route of same rubber brake hose from previous picture to hard lines on rear axle.
Passenger side close up:
Drivers side close up:
Metal tabs on either side of pumpkin that hold the hardlines to the rear axle make me want to say that these are the factory original hardlines as well the correct routing of the lines. However, I am not 100% sure, and the route the hardline takes to get "around" the pumpkin looks a little too sloppy to be stock.
I'm sure some else can chime in if they know more than I.