Would a car jack work?Height wise or length wise? If it's height I would try slipping a small floor jack into the frame and very carefully spread the bars apart while watching for cracks.
Steve
I only have to spread it a mm or so. Hopefully it will work. This tank is the most expensive part of this build.If it fits in the space it should. I'd wouldn't push it too far all at once. I'd watch out for tubing being crushed and as I said the tubing tearing where it's welded to the head tube.
Steve.