I am installing a FAST EZ EFI system on my mildly modified 350 powered '67 Chevelle. For the return line do I use the the original 5/16 fuel line or scrap it all and go to a 3/8"? For the tank inlet can I use the readily available 3/8" out 1/4" in sending unit or do I need to fabricate a duel 3/8" in/out unit? The car is simply a street car which is never raced so I am not interested in weld in sumps and surge tanks for this install.
Thanks for all the help everyone.

Just upgraded my fuel lines in my 66 from 5/16 to #6AN (3/8"). This should work for you. I drilled a 3/8" hole next to the 5/16" outlet on the sending unit and soldered a piece of 3/8" OD steel tubing I had left over from something. Used a plumbers torch and solder. Then I got a 3/8" compression to #6 Male AN fitting for the outside end of the soldered in tube. Ran #6 AN steel braided line up to the intake. Now I have the old 5/16" line still in the frame to use as a return line when I upgrade to EFI. I am thinking about the FAST EZ EFI for next spring. Would like to know how your install goes and what you think of the system. Could send pictures if that would help.

I have the 3/8 return line and feed line on both my cars. Was was going to use the charcoal vent in the tank as my return line in my Camaro but found out the hard way that its a one way check valve. I wound up pulling the tank and welding a nipple at the top passenger side corner.

Thanks for the info guys. I will let you know how it goes. Right now I am just getting the parts together to ensure the install goes smoothly. It looks pretty easy and basic having delt with sequential and batch fire EFI installs in the past.

http://home.insightbb.com/~jhanas1/FuelFitting.JPG

I have the 3/8 return line and feed line on both my cars. Was was going to use the charcoal vent in the tank as my return line in my Camaro but found out the hard way that its a one way check valve. I wound up pulling the tank and welding a nipple at the top passenger side corner.

I've used the 5/16 vent line on a couple of cars. On the first one I learned the hard way that there is a little cap on the end of the line with a pin hole in it. If you pop off the cap it will flow freely. That was on S-10 fuel tanks, others may vary.