I find the center line by marking the tube with marker and running a square along the edge.

I line the center of the holes up with the center line. Then I clamp with hose clamps.

then I drill the hole for the 3/16 rivet. (alum)

I use un-popped rivets to help keep things lined up.

Just me workin.

For prebuilding the tail I went ahead and poped one rivet in the center hole of each L-bracket. (or you could get a lot of hose

6 hinges total for the elavators