Fitting a '29 tank cover

I'm trying to assemble the tank cover and upper firewall on my '29 roadster. The tank cover fits well on one side of the upper firewall, but not so much on the other. The cover is a new Brookville piece, but it looks like the radius is off on one side. Where do I start to fix this?

 

Any thoughts before I start cutting??

 

Grab the vise grip clamps and pickup the hammer and dollie,,,weld it in place. HRP

 

Before you start cutting or preloading the parts together, you need to first confirm that the upper firewall is symetrical. Trace the passenger side upper firewall curve onto cardboard, cut it out, then hold it against the drivers side. This will tell you if the upper firewall or tank cover are mis-shaped. The lip on the upper firewall looks a bit wonky and crude. Is it also Brookville?