My 57 3200 had the same problem only worse. I couldn't find anywhere to get patch panels for this so I bought a used roof from JIMBO59CHEV in the swap meet forum. He sold it for a good price and it was a very good panel. Other than getting a used roof or making your own patch, I think you are stuck. If someone knows where to get a repair panel jump in here, but I couldn't find one.

1957 Chevrolet 1/2-ton Stepside LB in the Gallery
My Photobucket shots

The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself." - John Stuart Mill (1806 - 1873)