Rear Brake Line Installation Help

[DKSpringer]

Hey all. Looking for a little rookie help here. Found a drip in the steel lines, as well as some evidence of previous owner "tweaking"..... So I bought a set of pre-bent lines for the rear circuit from Inline Tube.

For anyone who has done this before, how did you install the line from the proportioning valve back along the frame rail? Looking at the obstacles I have to go around, I'm not sure how I'm going to get in there without significantly un-bending my pre-bent lines, which kind of defeats the purpose. Any tips? Do you snake it in from the front, underneath the radiator? Straighten the line and poke it forward inside the C-channel?

Truck is a 1977 K20, but I would think all of the 2WD trucks would have a similar challenge, although with maybe a little better access.

Help Please!