One can find hitches that are rated for more than a given rig is rated to tow! I had a 96 CC GM, I was pulling a 6500 TT with WD bars, and an equipment trailer with a pintle hitch that was dead wt attached! at around 9000 and 1000 lbs of hw. Went to Tork Lift which is down the road from me, told them the trailers I was pulling, put a hitch on it that will handle said loads! Oh yeah, the truck was only rated to 7500 lbs or some such goof ball thing! so any way, hitch did fine for 10 yrs and 200K miles, even when I added another piece of equipment ont he trailer that took me to 12K and 1500 hw!
I would also NOT weld to your trucks frame, many of the LDT trucks frames are not able to be welded on and retain structure. If you had an mdt or larger, then many of them are weldable. Going to a stronger larger diam bolt would be your best bet for some of what you need. The other is to figure out if the steel is thick enough or the proper type for what you want to do. Along with, it is what, 20 yrs old?!?!? it may be fried from use! I could be wrong on that one too.
I personally would not worry about what you are doing.
Along with, the insurance WILL pay out if something happens, just as it does with a DUI or equal!
marty