I've installed one of them so far on my 7. Had to enlarge the big hole as stated, but the rivet holes fall out right in the middle of the flange. Edge distance looks small at first but it's not a problem; loads are minimal on the flange.
Opening the hole for the larger flange was aided by drawing up the hole pattern and new hole size on the computer, and printing it to full scale. I cut the hole out of the paper, clecoed the paper to the tank, and used it to shape the hole. If anyone's interested I can make that template available.