The bondo will fall out in no time being soaked with gas...You can cover the hole with JB Weld and then coat the inside of the tank. Lots of threads on this site about cleaning and repairing tanks.
185s isn't close to being rare....they are all over the place...you can get anything you need for them. Your wanting to do a full resto? I have only partially restored my 185s and I have over 1000 bucks in it. This is a hobby that goes from cheap to expensive very fast...for now you may just want to get it in shape to be a rider.