On my 800 I had a bad exhaust leak between the manifold and exhaust pipe. It was creating an erratic idle. Ordered a new gasket from the local New Holland dealer and gave it a go. During the restoration I had used brass exhaust nuts fortunately. The outside nut and bolt came out easily. Then the problem began. How to get a wrench on the bottom inside nut. I tried contorsion, cast a few spells, nothing worked. Finally, I took the cheapest 9/16 box end I have and cut it about three inches long, then clamped it the vice and gave it a slight bend. Worked like a charm. Slipped easily on the nut. Maybe this will help someone.