I watched your video, if it makes you feel any better, I had the grind some of the retainer tabs on 40 DCOEs, it's not just because you were trying to fit them to 42s.
The other thing as you mentioned, the ram stacks position and hold the auxiliary venturi on the 38, 40 and 42 DCOE so at the very least the sleeve part of the stack that sticks into the carb body between it and the auxiliary venturi needs to be in place if one were to decide to just lop off the stack above the ring for the retainer tab, not that I'm recommending doing so. Those APT 16mm stacks are the only ones that I know of right of hand that work with the short K&N oval filter set up.