Tonight's task was to clamp one of the spar cap (stiffeners) to the inner flange of the forward spar of the horizontal stabilizer, and then match drill all of the holes. The holes on the spar web were #30, while the holes on the spar flange were #40, and there was a bunch of deburring of the holes in between the two operations to ensure that there was a completely tight match between the surfaces. I was initially concerned about the amount of bowing/bend that was in these spar caps as they had been delivered from the factory (the instructions mention that there would be some bend), but they clamped quite flat against the spar just fine.
What's next? Repeat the same steps for the other spar cap.