This topic has been covered before, but I found an easy way to spend practically nothing to plumb up an LS engine with junkyard fuel lines, without using heat or boiling water, and no tools other than a hammer.
Been helping my brother with LS swap into his 65 post 300 Chevelle. Last month we went to the local Pull-a-Part and scrounged $20 worth of nylon fuel lines and fittings from a 95 Caprice and a mid-nineties Caddy. Took the removal tool with us and salvaged all the push-on connectors undamaged. Also salvaged the plastic clips that route the 2 lines alongside each other
Working from the engine back toward the tank, we measured needed length to run down the driver side frame rail to a GM fuel filter and then on to the tank. Did the same with the return line. After choosing the best lines, we needed to install 4 new connectors. None of our local parts stores stocked these, so I decided to try to re-use the original connectors.
First, I picked a 12" section of 2x4 and sawed in half along its' short dimension, giving me two 3/4" x 3 1/2" pieces. Clamped these together in the vise, and drilled 2 holes along the split. One hole is 11/32", the other 9/32". This gives a perfect fit to hold both sizes of fuel line in place while installing connectors.
Now, to salvaging the original connectors. Cut the fuel line about 3/8" below the connector barb. Using a pair of side cutter pliers, make a single snip in one wall of the line back toward the barb being careful not to nick the barb. Using the side cutters, slowly peel the line diagonally down toward the barb. The line will continue to split as you work down and around toward the connector end of the barb. Using this method, I salvaged all needed connectors without damage.
Installation is a piece of cake. Use a sharp single edge blade to make a square cut at the desired place on the fuel line. Clamp the fuel line into the 2x4 with a vise, with just enough line sticking up for the length of the barb plus a smidge. Remove the inner clip from the connector, and lube the barb lightly with WD40 or whatever lube you have. Start the tip of the barb into the line by hand and use a wood block and hammer to tap the fitting in. Take care to hold the wood block square, it only takes 3 or 4 taps of the hammer to fully seat the connector barb into the line. Re-install the inner clip and remove from the vise. The 2x4 clamp leaves no marks on the lines and the re-purposed connector looks exactly like a factory install.
We literally plumbed the entire car with $20 worth of fuel lines and about $5 for clamps. I'll try to post some pix of the procedure later this week. I hope this helps some of you guys trying to save a buck using factory fuel lines.