Here is my method for building the aileron counterbalances. There are two little angles that form a channel and rivet between the counterbalance arms that have matched holes to the arms. The trick is that the ribs do not have the holes yet, but need to line up with the angles. Can't cleco them on. I used some 3/32" pop rivets as a temporary fastener. In the picture below, the arm on the right has just had two pops set. The left arm has one rivet tail that has been sanded down near flush. It's other pop was first sanded, then I used a #30 drill on it until it was just flush.
These rivets are strong enough to hold the parts in alignment. I clecoed the arm together without the ribs, blocked it up, and witnessed the 3 3/8" height to the top of the arm:
I then added the ribs, and used a straight edge to align the front flange of the ribs to the angles:
After I had a couple gnu-vise clamps on I flipped it over and added another on the other side. Dissassemble, transfer all the holes except for the pop riveted ones, dissasemble more to deburr, remove pop rivets, reassemble, and get the last two holes where the pops were.
Need to drill the lead block holes to final size, edge finish, then it is time for the chief riveter.