Final drilled the holes for the LP4-3 rivets. I used these little rivet hole finders. They fit into the existing rivet hole. You lay the undrilled angle and cleco the part in place. A little tap on top of the hole finder and it marks the exact location of the rivet hole with a little punch.
Here’s the little hole finder in place before clecoing the angle in place.
Here’s the little mark it leaves. I checked and I will have enough rivet clearance even though I hogged out quite a bit.
Angles riveted in place. I primered the bottom of the angle as well.