Colin, thank you. I have an offset wrench but it's a 12-point and I think it would strip the nut (I tried it anyways and it slipped right off); I searched high and low for a 6-point offset wrench, but I couldn't find one that was sold anywhere local to me.
I don't have an impact gun, so I can't do that either.
More about my trouble with this: when I put my breaker bar on there with a 17mm deep socket, I can feel that I'm getting the leverage I need. The problem though, to be more descriptive, is the whole strut assembly begins to torque (like a twisting motion) when force is applied to the nut of the top hat. I don't have a technique for neutralizing the strut assembly while doing this; I thought a vice would do the trick but I was wrong.
With all of that said, it sounds like an impact gun would take care of it. The only problem with that is they're expensive. Man, I wish I lived in Cali so that I could visit your shop and knock this out of the park.
I really appreciate your ideas, though. Even if I couldn't use them per say, they illustrated the concepts to me and gave me ideas for tools to buy in the future. So not all was lost there.
I guess I'm going to throw in the towel for this part of the job. I'm going to take it to a pro tomorrow.