if your's fits where you want, just modify it. You can get a kit and weld it on.
Hate to promote summit, but here's a link to the kit. Jegs will have it too, but I'm currently shopping on summits site for fuel line.
If your current one is plastic then you'll be looking at swapping it out. If you're looking for a custom one, I've had a couple made by fuel safe, but they get pricey. No real reason to re-invent the wheel though since there are a lot of options for these trucks. I'm actually installing a 69 camaro tank this weekend in my 70 c20, so many options.