I had the same problem with the roof. I changed the roof just like your shop guy said. If you cut the good roof off the one cab & weld it to the other it is easier and cheaper than the other way around. I have a lot of PICTURES HERE from when I did my roof. You can PM me if you want to ask any questions about it.

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)