[chris vickery]

Looks like you new parts truck is pretty good for a restoration!
It apears that the bttom of the cab sheet metal is toast like most are.
On my cab 12 Ford, I stripped off the sheet metal skin and had the bracing and angle iron framewoork sandbasted clean. I reskinned with 18g which was very simple and plug welded through the bracing and framework. Turned out great. A lot easier than piecing in metal and bodywork.
The upper cab part presents more of a challenge if the seam is rotted out but it can be fabricated as well. I did one roof where I removed the rear skin where it was spot weld to the top and made a new skin up. The tricky part was the flanged joint where upper and lower cab section meet. A handy guy with a sheet metal brake can do it...