There is one problem with the idea of drilling holes top and bottom and using a bolt through both sides of the frame. When you tighten the bolt down it will put stress on the frame and start to compress it.The compressing of the frame will happen over time even with out the bolt being over tightened, the twisting and flexing of the frame will cause the bolt to have to be constantly tightened to make up for the compression of the frame. In the end you will have a crease in the frame needless to say this would be disastrous under heavy stress (such as a motor vehicle accident) the jeep could bend almost in half.
If you use a bolt through the frame the suggested way you will have to use a piece of pipe inside the frame to counter act the crushing action of the bolt and yes it will have to be welded in place.
I used large bolts welded into the over sized holed from extracting the the old bolts as I read was suggested earlier on.
This was much easier and a better fix than the bolt through the frame idea.
I can see why long a blot through the frame idea was suggested such as if you cannot cut and weld, but I think you will be much happier with the end result if you do not use this method.
Even if you have to have someone that can cut and weld do it for you, the outcome will better then using an bolt thought the frame.