I tried at the top rear of the engine and so far no go. It's too far down for my hands and no tool that I have, and I have many, will fit enough to turn the nut. There are many different styles of wrenches available today, I'll have to look into them. I can get a long box wrench over the nut but it does get onto it enough and there is almost no room to turn it. You can't even get in there to twist or break it off. Going to try from the bottom and then decide what to do.
Called the tech at Dorman and he said that when he worked at GM they got the nut off from the top, very hard, very slow. I can't see how unless they had a special shape wrench.