is this more on the line of what your thinking?I still need to drill the holes to plug weld but I wanted to get it fit first.Here's all the pics:
But try using a cardboard template and then test fitting and trim so you get the whole covered. Tack weld in place. Put some holes in the sheet metal and rosette weld it all around and then seam sealer, spray paint and some undersealer...never know it was done.
Pattern and cut piece
Outside the cab - see the holes for welding
Inside the cab
Hope that helps.