Finally, I am assuming you already have a gas tank filler-neck gasket on your truck. If not, you'll need to buy one. I got mine from GMC Paul's (
www.gmcpauls.com). It was somewhere between $5-10, and their service is great... I'd buy 20 more if I had a use for them
Put a small bead of silicone or similar sealant around the bolt to prevent leaks from happening (thanks, cdowns!). Slide the bolt into the cap, and place the cap over the gasket as shown below in the first picture. From behind, slide the bar over the bolt, then tighten down one of the nuts on the back end. once the first nut is tight, take the second nut and tighten it on top of the first one, then tighten the two nuts by twisting opposite of each other. This will keep the nuts from falling off by locking them together. Double-nutting is a great way to secure stuff.
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If I've got anything up for grabs, it'll be here: 7-hole gauge cluster for a 67-72 p/u FREE (
link)
I can't check the forum daily. If I don't reply to you within 24 hours,
drop me a PM! I'm (hopefully) still alive and will reply faster to a PM.