OK, I think I misunderstood you at first but thinking about it now, (and having a glass of wine helped) I might have some answers.

I didn't take that bottom brace off, but I did, manually, move the whole head assembly up, out of the way. I just turned by hand the brass bits on top of the motors until I had clearance for the big metal box to go through the uprights.
Once it was all screwed together, I put a level on the bed, then on the top chrome bar that the head assembly moves on. I manually turned one side or the other to get those bars horizontal. Then I leveled the bed, then I did the head leveling again. As I said in the last post, all in all in took about 15 minutes to get it all done, and I do a bed level every morning before I set the machine to work.