After preparing myself as much as possible for the challenge, I started using the double-offset rivet set to drive these rivets that attach the inboard ribs to the forward spar of the Horizontal Stablizer. This type of riveting is always challenging for me and I usually end up having the attempt some of the rivets multiple times before I'm satisfied with the result.
After those spar rivets were done, I started using the hand squeezer on the AD3-3.5 rivets along the inboard edges and tips of the HS. These all proceeded without any issues, other than some clearance limitations in a few places where the lightnening holes in the ribs.
What's next? I'll have to use the air rivet gun to drive all of the remaining flush rivets in the skin, and then I'll join the rear spar assembly on.