2 x 3mm steel plates next to the ears and a large bolt and nut placed between them should allow you to jack the sides out - unless you have access to a hydraulic ‘birds beak’ spreader that they use in body repair. It’s a bit tedious but you are always in control. It will move out and spring back somewhat, so you have to go further than you think to allow it to settle at the required dimension. Needles to say it will crack the paint and might even leak! Unfortunately we need a pic of the whole tank to make doubly sure it is a 400/4 tank before you start any alterations.
Ian
