The 3/8" line ran under the upper a-arm to keep it away from the 348 and 409 manifolds. If you already have the 3/8 line running back to the tank, you can buy a new line and splice it into your existing line. Actually, the 3/8" line is jointed with a rubber hose about where the frame starts to bend up ward (just under the firewall). I think you can buy just the front section. You might want to get the clap that holds the fuel line to the frame. Its a metal bracket and a fine thread bolt. You can rob one off a 327 car in a salvage yard, if its not available new. I think that the hole is already there, just needs tapped. Its mostly hidden by the upper a-arm.
With my old 63 SS, I installed a 409 where a 283 had once been and I was having problems with the fuel getting too hot. The car would start to sputter after about 10 minutes and then would die. I re-routed the fuel line and it never happened again.
Best of luck!
Ross
