I've changed out the fuel line on a 65 Fastback and it was very simple with the parking brake, exhaust, and driveline off the car. I had access to a lift which helped. Do you have a good set of jack stands? I would recommend picking up a fuel line clip kit and apron fuel line grommet.
Not to bad, I am 90% through an I6 to V8 conversion and just replaced the I6 fuel line from the tank to the engine bay with a V8 line from the tank to the engine bay. You will need to purchase replacement clips, since the majority of them are one time use only. The clips are a bit of a PITA to get out if I recall, and to install them, just use a pair of pliers and squeeze the butterfly together. I did disconnect my rear brake line, the flex section and made it a lot easier to manuever the removal and replacement line in that area. In addition, don't forget, you will need a new section or rubber fuel line, about 3" or so, that goes from the tank to the line........the old one may be the origional. Mine was pretty dry rotted, surprisesed it did not leak. I went with stainless steel as a replacement which may be overkill since the car never sees weather anymore. As for the pre-bent lines, they are 99% correct ot all the contours, my replacement V8 line was not as snug in a section you will not have to worry about with the I6 line replacement. If you are like me, doing it in your garage with no lift, a lot of work on your back an car on jacks. You will say a few choice words during removal/install, but very doable.
I did my 67 laying on the floor in my garage so it's not bad.
The only real tricky part is getting it up and over the rear end (jacking up the body helps) because it's so long that when you're trying to twist it around it catches on the front tires. And the transmission. And the e-brake cable. And everything else under the car.
You'll probably need to tweak the bends just a little, and like everyone's said you'll likely need new clips, but it's nothing to be worried about.
It's harder to "unfold" the line from the shipping package than it is to install it on the car, LOL. Do the "unfolding" inside your house, preferably on carpet, in your stocking feet, walking the loop out of it.
I agree with Magnus. Anything under the car is going to give you grief. I think my biggest problem was routing it around the parking brake cables (I may have had the brake lines out when I put the fuel line in).
Please be careful... Don't forget you're working with gasoline...and if you decide to raise the car make sure the Jack stands are set properly and not too high. The raising will help a lot to work easier and see everything. hope you're younger than I am.