His other post says he has a couple of 64 Impalas. If that is the case, we just need to know what engine. If memory serves, the 3/8 line was used on the 327 (perhaps only the 300hp version) and the 409's. But I think the 409's had a return line to the tank as well. I don't know the 409 as well, so perhaps somebody can correct me on that.
In any event, your shop manuals should have that information. You need the 61 shop manual and the 64 supplemental shop manual to be complete.
I am not sure if these will help, but my 64 started out with a 283 and I restored it with a 327/300 (bored/stroked to a 383).
Please verify this info, my memory is getting fuzzy 10 years after the fact, but here are some photos that might help.
I seem to recall some tricky business with the routing of the line between the frame and passenger side upper control arm. The 283 with the smaller line, did not take the same route.
Close up of the fuel pump area and fuel line going under the control arm
Fuel pump to carb routing. Note, I used a carb from a 409 due to the bore/stroke to 383. The 409's Carter AFB carb has the fuel inlet on the driver's side rear corner of the carb. The proper 372/300 Carter AFB has the fuel inlet on the front of the carb, on the passenger side. I made a line to go from the stock position to the other side. With the air cleaner on, you never see it
It has been 10 years, so I am not sure, but I think this shows both old (283) and new(327) fuel lines (and the brake line). If memory serves, the 327 has the line going through the drive shaft tunnel, while the 382 did not.
Thank you responding. That's just it The 64 I'm working on has a stroked 350 with a Muncie 4 speed. The gas line I purchased from classic industries and came in 3 pieces. I was hoping that someone out there might have a picture of a rebuild that I could look at and help me with installation. Sorry for the lack of information in my part any response is a help thank you for your time