[Greg Reid]

In the approximately 10 years that my tank has been installed I have had to wrestle with getting the filler cap off and on because about one-third of it was below the bumper opening and the bumper itself was only about a half inch from it. I had to rotate it and then rock it back at the top, slip it out and reverse the procedure to put it back on. This was AFTER forcing in the neck up as far as I could get it using a bumper jack and a block of wood back when I originally installed it.
Last week my fuel sending unit crapped out and while the tank was out I wanted to re-examine this issue. I happened to lie it down at the base of what is about a 45-degree embankment away from my garage because it still had two or three gallons of gas in it.

What I discovered is this - If you brace the front end of the tank up 14 to16 inches or so and get the filler neck almost parallel to the floor you can easily brace your knee or probably even your palm against the top of the tank right above where the filler tube enters it and pull the tube up with firm, even pressure, it will easily move the 1 to 2 inches you need for proper alignment with the '68 bumper opening and never need the much harder to move neck to bend.
You'll never get that bent by hand to match the original 68 neck.
If you lay it flat on the floor you'll be wrestling with the tank trying to keep it down as you put upward pressure on the neck. The angle apparently focuses or concentrates the force better?
It moved so easily that I'm just thankful that I didn't yank on it. It probably would have caved the front of my tank in. The amount of actual tank sheet metal movement needed is very slight to get 1-1/2 inches of movement at the end of the tube. Totally undetectable.
It really surprised me that it moved. I was just probing.
Can't attach a picture right now for some reason.