After drilling the elevator horns I placed the horizontal stabilizer HS with the elevators on the fuselage. It is really looking like an airplane now. I clamped the HS in place and then measured the distance from the end of the HS to the firewall on both sides of the firewall. It is perfectly square. I tighten the clamps tighter to ensure it did not move.
To mount the HS permanently to the fuselage initially I have to drill two bolt holes. The holes run through the HS structure through the longerons of the fuselage. However the longerons are not visible from the top of the aircraft. After assembling the aft fuselage section I made marks on the structure showing where the longerons are located. I transferred those marks to the structure of the HS showing where to drill and where the edges are located. I have to hit the center of the longerons to ensure edge clearance. You can see those marks in image three.