Stab mounting
The manual explains the procedure for the composite stab; for the balsa version, simply skip the steps about sawing the elevator from the stab and making the cutouts where marked.
The stab is held in place by two rods on each stab - one forward one which is carbon fibre - it simply slips into a maple block and is retained by tightening a 4/40 machine screw against the rod. The rear rod is a combination of metal and carbon fibre, and has a much more elaborate retention mechanism (as will be seen in subsequent photos.
The fus is pre-marked with the position of the holes for theses rods. For the stab, the position of the forward rod is likewise clearly determined by the hole in the plywood rib, but we need to be fairly careful about drilling the hole through the other ribs, blocks etc. It is important to get the rod perpendicular to the rib in both planes. I found that the easiest way to accomplish this was to make up a simple jig - drill the appropriate size hole through a 1" deep piece of hardwood, using a drill press to get the mutually perpendicular alignment correct, then simply place that block on the root rib and drill through it, as shown in the photo below:
(BTW, note that for the elevator, the position of the control linkage does not match the position shown on the main detail plan. So, you may want to make a note of the position of the cutout in the 1/32" plywood elevator centre, so that you don't try drilling the hole in the wrong place)