....the dim from the bottom of the bbl channel to the bottom of the RR groove is called the web and yours is way too thick......3/16" is max.
Fred, I think you meant to say "....from the bottom of the bbl channel to the
top of the RR groove...."
Chris,
Based on the ink stamping on the side of the stock, I'm guessing it is pre-carved stock, or at least the barrel was inlet and the RR hole was drilled by the stock supplier. The nose of a large Siler lock is about 1/2" wide, based on that, and if your markings are correct, in the picture it looks like your web is about a 1/4". Not optimum, but if the hole is already there, you need to work with what you have.
I think you can rotate the lock plate (use the touch-hole as the pivot point) to bring the nose down (and tail up) and put a #6 lock screw thru the lower part of the web, just grazing the top of the RR channel. If the screw hole in the lock plate ends up being a little above the center line of the lock nose, it's not the end of the world, the frizzen spring will cover it.
Ron