[767Jockey]

Guys-
I found a solution so obvious it's amazing I didn't see it sooner. By dropping the lower A arm mount out of the bottom of the chassis upright that the nut in question is in, the entire bottom of the upright is open. The nut is about 10" up from the bottom. By purchasing or making a long reach wrench, I can simply reach up and hold the nut while I tighten it. How I didn't see this earlier I'll never know.