It looks like from the picture of the inside of the cab that the roof may have been replaced at one time. It looks like someone welded the upper & lower inner panels in the seam. I agree sandblasting is the way to start.
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)
