on my 73,im assuming that the larger copper line with screen in tank is the supply line and that smaller copper line is the return and that if i have carbs,the smaller line is not needed., and can be blocked off.?

Correct. A piece of modern fuel line, a shouldered bolt w/clamp and you're good to go.

While there are more elegant ways to do this - I did the exact same thing years ago. Like any fuel line inspect the clamped line regularly.

So, I only need to have the single line from tank to the rear of the car….?

If carbs only one line is needed, FI needs a return line.

A return line with carbs keeps fuel cooler and helps with boiling in extreme heat.

Check my gulf blue thread. I just posted a photo of the regulator I i stalled for the carbs. I've got a feedi e from the gas tank and a return line back to it. Fuel will continue to circulate and the regulator pulls off what's needed for the carbs. Keeps the fuel cooler and stirs the tank

I just put both in, that way if i ever swap to something injected and overhead cam....

Not to bogart your thread, but...do you run 9mm line from the tank to the soft line that goes into the tunnel then use 7mm in the engine bay?

I measured a supply nipple and it measured 10mm O.D. The return nipple was 8mm. This would be the case for 70-74 cars and 75-76 cars used 10mm on both gas tank nipples.

Lines for the engine compartment are 8mm for the fuel loop hoses.