My apologies! I was wrong on question 1. I had in my mind a different setup.
1. I don't think it has to do with access to the rudder horn. I don't know why those 8 rivets are bucked/squeezed until after the LP4-3s are pulled and the R-00910 Horn Brace is locked down too. Perhaps it's related to promoting the R-00904A-1 Bottom Rib to better line up with the R-00904B-1 Bottom Rib and R-00910 Horn Brace prior to locking things down?
2. I see now what you're referring to. I don't see where in the plans that rivet between the trailing edge and the attach strip is placed. It certainly should not be done prior to 7-10, Step 2.
With respect to the LP4-3 next to that flange of the R-00910 Horn Brace, it's tight in there. But those LP4-3 are really flat. I took a picture of that area on my "surplus" rudder to show you what it looks like. BTW, I believe "LP" stands for "low profile". I believe they are manufactured by Avex
One thing to watch out for is at the skin and Horn Brace. Make sure it fits well in there. This is what can happen if it doesn't
. I had to address that potentiality prior to assembly on my first rudder
, but not my second. Image below by HeliCooper