It is covered in ice right now. I will try to pull it out of the bed later today and let it dry.
But, the best way to fab the cab mount up is like this:
Remove the top 8 bolts that are located on the back of the cab behind the driver and the drivers side grab handle.
Tape a sheet of poster board to the corner of the cab and let it overhang the bolt holes by about an inch.
Use a small ball peen hammer and gently tap around the bolt holes with the round end. Once you feel you are in a hole, tap harder and the poster board will cut itself out. Do this for all 8 holes.
You can also just stick a pencil through the holes from the inside to mark the holes and then punch them out later. I like the ball peen hammer method better because the true hole is now there instead of just part of it marked.
Cut off the rest of the sheet at least an inch toward the door from the grab handle. Use either the ball peen methord or a pencil from the inside to mark these 4 holes.
Depending on the size of poster board you used, you will also need to trim the bottom of the sheet off about an inch below the last row of bolts on the back. It doesn't matter where, you just don't want it hanging down below the cab and you don't need it more than an inch below the last row of bolt holes.
Untape the poster board and transfer the edges and holes to a sheet of metal. Drill the holes, bolt it to the 8 holes in the rear and bend it around the cab until you can put the grab handle back on. Mine is two pieces of 3/16" or 1/4". It doesn't need to be that thick. Wrapping around and living next to the cab will make a piece of 10 or 12 gauge plenty thick for just one light on a pole. 10 or 12 gauge can be bent by hand or "helped" with a few light hammer blows while you are bending it.
Mounting the pole is going to be the head scratcher. A 4 inch x 1/4 inch strap welded vertically to the now bent sheet metal will take away any flex not already gone and give you plenty of room for the mounting system of your choice. Anything from muffler clamps to Briggs and Stratton connecting rod ends can be used to hold the pole to the 4" plate. It all depends on what you have access to and what size pole you are going to use.
Does this help any?