LightSpeed, sorry. That was the stud that mysteriously disappeared so was not an issue. If I remember correctly when I had to do the other side so ling ago I used a narrow wood chisel to get in there and start it.
Thanks Michael, I tried that, I tried a long sharpeded screwdriver and it didn't budge because it is bent around two faces of the nut. I can get under on face but not the other. At this point I am considering using a Dremel with a burr grinder, like a dentist, to carefully carve away the offending piece. Why MMC thought it necessary to bend that plate around two sides of the nut is beyond me.
UPDATE: I carefully cut the locking plate away from the nut on the exhaust stud. It worked and I was able to remove the nut. What was interesting when I removed the nuts was the bottom nuts were fairly tight where as the top nuts were almost loose and took little pressure to unscrew them.