I worked at a hitch shop for a couple of years. I have cut- off numerous hitches that were "welded on" after the welds failed. I have never seen a bolt-on hitch fail (except one, but that was a legitimate case of retardedness). No hitch maker makes a weld in hitch for a reason. frames are dirty, and rusted, overhead welding is difficult, can it be done sure. do you want to do it no.
Do not bolt it. spend 140 bucks, go to a hitch shop, and buy the right hitch for your truck. it will come with the right bolts.
you will have to drill 8 bolt holes, and then tighten up 8 bolts. You can do it in under 20 minutes if you have a standard plug- in drill and a 1/4 and 1/2 inch drill. Keep in mind, that hitch manufacturers put those bolt holes in particular places on the frame rail where the strength is sufficient. I'm not saying that it really matters in your case, but you really dont want that liability on your hands.