Drilled the four pilot holes. Cut the 4" hole. Enlarged two pilot holes with 3/4" step drill as indicated. Deburred all holes and cuts. Scuffed with scotchbrite.
The riveting of the VA-187 flanged duct has been a nightmare as the riveting with the bucking bar results in warped flange. drilled out few rivets, but got three enlarged holes. Used the squeezer and slightly better result, but still some ondulations are there....I had to use -5 rivets as the holes were too big for the -4 rivets. Not super happy but it will work.