What I did on my 67, not the same but similar enough was basically what Keith Mopar did. I raised the tank into about the right place, then inserted the lubed up filler tube and raised the tank making adjustments to the filler tube as I went.
Also, make it easier on yourself remove the vent tube completely.
Don't forget the floor gasket , reinforcer.
This all relates to 67 but I suspect early a were very much the same.