After another small battle today, with a bit more grinding, I got the tank bank on.
I was very concerned about the left side bolt, the thread is not in great shape and any back pressure would likely cross thread it. Still a drama getting it started. Took about 4 attempts, removing the tank each time to check the thread was still OK when the bolt did not feel like it was getting started properly.
Here is a photo of the washers now ground down, with the fuel take in place.
Also; fortunately the breather pipe nozzel that broke has a metal insert, so a bit of superglue at the base of the plastic nozzel saw it back in place OK. No doubt it will break again next time I remove the breather pipe.