Well, it depends on how you want to run the numbers. If you are trying to stay within GVWR you are not going to make it. You only have less than 1k# payload available using the GVWR yard stick.
However, if you use your rear axle weight rating as the yard stick and guessing your actual axle weights based off your measured GVW (assumes rear axle weighs 3100#) then you have around 3000# available and assume you will carry an additional 500# of stuff in truck you would have about 2500# for pin weight. That is approximately a 12,500# FW which is doable in a small bunkhouse. You would definitely be over GVWR but under axle weights and GCWR. The GVWR is a warrenty item only (there is no legal requirement for GVWR nor GCWR) and since you are out of warrenty any way that is not a problem
You've got enough engine, transmission, axle, brake, and frame for 12,500# FW just lacking on manufacturers GVWR for those year of trucks.