Hi Ian,
One bit of advice: Try to get it out without damaging it more than necessary. If you hack it into pieces bent and molested, even a good sheetmetal man cannot get the correct shape. If you can take a tape pattern of it, preferrably before taking out the old panel, you can send that to Masachusetts or any other place to have the panel made. Go to
MetalMeet - for Metalshaping Enthusiasts & Professional Metalshapers. I think you have to get a login to see the posts. Then go to "Metalshaping Tutorials" and then "Making a flexible shape pattern". If you have a lot of rust holes, cover them with aluminum HVAC tape first. After you have the replacement whether you make it yourself or get it made, then you cut out the old one. If you're patient, I'll get to that in this thread, because I have to make several parts for mine where I will use the flex tape pattern as a guide to get the correct shape. Then after the shape is right, contour patterns will help getting the arrangement right.
If you whack a piece of metal sheet with a hammer you get a pucker in it, you have changed it's shape by stretching You must shrink it to get it back to straight. If you roll it up you have not changed the shape, just the arrangement, you can unroll it to get it back to what it was.
The Spider was placed on the bedsheet folding machine frame today. We levelled this frame using a machine level accurate to 0.3mm/m. Some quick measurements indicate the car is not as crooked as I feared. We're talking 5mm or thereabout. I'm not so sure they were more straight out of the factory.