All I've seen is a couple of excellent photos of the sight. It's from the real fancy J. Kuntz rifle in the MET. I doubt if Tom dared to flick the sight leaf up, so that will remain a mystery. However, on my rendition, friction alone would not have served,so i added the little flat leaf spring.
yes, there is a lot of barrel steel bumped up to create the dovetail, but even more on the original. I used a sharp cold chisel and a heavy hammer to raise the metal after cutting the rectangular slot, finishing it with files. Advantage...it's cool to start with, historical, and an easy way to maintain a tight dovetail. Notice the witness marks on the sight and barrel both front and rear.
And Jerry, it's not coming off the rifle, even for you. I mounted the sight way down the barrel, and it's crystal clear for me - for now. I love shooting this little bird-like rifle.