This is done by aligning both elevators and then drilling a hole perpendicular through both horns.

As suggested by the instructions, we made a special drill guide (not on the picture) to clamp between the two horns.

Then the HS was put onto the fuselage and positioned according to exact measurements. Then the 4 bolt holes for the HS front spar are drilled to the underlying structure. Using an extra long drillbit makes it easier to drill vertically.

Marking the position for another one of these holes. Edge distances for about 3 angles have to be taken into account.

After the bolts have been positioned, 2 spacers are made from a stock aluminum bar. The spacers are then drilled to the recently drilled holes on the front spar assembly.

After aligning the incidence angle, the HS rear spar bolts can be drilled.

And that's how the HS center front spar looks like with all 4 bolts and the spacers in place.

Now it's starting to really look like an airplane :-)
We had to remove the red metal sawhorse that supported the fuselage in the back as it was located where the elevator control horns are now.

Some more work required before the VS can go on.