Hello Terry and welcome to the site.
You might consider making a set of tucking forks to do the shrinking on your gas tank like these.
https://www.youtube.com/watch?v=mNSTxHmXmTg
If you are going to modify a HF bead roller, here are some mods I have made to mine.
https://www.youtube.com/watch?v=Ra2-A-IuT-Q
Jere