removing gas tank: I'm having a similar problem
You may want to try and clean it in place if possible. According to the shop manuals I have: yes, there is only the one bolt holding the tank on, however the hayes manual states that getting it out of the frame should be avoided if possible because of how involved the process is.
(might be easier on an '83)
dual seat, side panels
probably fuel tap as well
and any other obstruction (tank is removed through the rear)
I will unfortunately be undertaking this process on my new/old '81 GL1100, if I have any luck I'll let you know.