
I just did it on my 52 by removing the whole frame bottom. I think handbrake cable routing changed in 55 or so, so I don’t think the front half of the gas line is routed exactly the same as this shot. If you shine a flash light through the tunnel you can probably see how the front is held in. I think the gas line always runs through tabs so you might have to make a long prying tool to open them up enough to pull the old line and pass the new one through exactly like stock.

Note clip towards the back that holds the line to one of the handbrake lines.

This is what the early tabs look like.
Also FYI the tubing is supposed to be 6mm OD and .8mm wall.