I did this step a little differently than the plans specified. I didn't make any changes to the layups, just how the jigs were laid out. I used the edge of my jig table, clamping the jigs to it. I also drilled 1" holes in the jigs, 1" from the edge, then used C clamps to clamp the three pieces of spruce against the jig. I'm not sure how well the nailing method works, but this worked great. It allowed me to get the longerons tight against the jig and to easily adjust the clamping pressure.

Here's a view of the whole thing set up, this time the left side. I put plastic wrap on the table and used small rectangles of cheap plywood (left over from the temporary firewall) covered with box tape to keep the clamps from sticking to any epoxy that oozed out. I didn't have enough clamps to do both sides at once, but, this worked well since I usually only have an hour or two to work at a time. Where the jigs were thin I simply clamped across the jig - no need to drill holes there.