I had to modify my 1971 filler tube to clear the full wheelwells I had added with the chassis work, I ended up having to replace the original tank several years later with a new one from Spectre after damaging the original one I ordered a new filler grommet also.
That was bunch of years ago, it was a hassle but I did get it by using some wheel bearing grease on the tube and grommet and determination to get it done.
I'm thinking I had the straps loose until the tube would fit properly, I didn't look in the FSM so maybe I got lucky on making it fit in their with the twisting and shoving
You can do this
If the factory guys and gals can do it you can to
Don't stop until your happy