[Lowell W]

OK...You said the nut is about 10" away. Can you get a wrench on it and tighten the bolt enough to hold it in place, then have a friend come over with a stick welder and tack either side of the nut up inside from where you can see it? Even a portable welding service shouldn't charge you much to come out and put one little "BZZZZZZTT" on each side of the nut.

Might as well do the same thing to every nut you can see while you're in there.

As an alternative, you could stick a wrench up in there, back the bolt out of the nut, then have somebody weld some "wings" on the nut or something else to keep it from turning, then replace the nut on the bolt.

You'll get it...

Lowell