That looks really cool! I would straighten out the upper cock extension, the thumb tab or whatever the heck people call it. The shaping of the Siler is like a neon sign that screams 'Siler' and most originals of any era have a much straighter extension, even those with some back bent curvature do not seem to display the abrupt bend there that the Siler does. It's pretty easy to do with some heat and then some filing, no need to add material at all.
I kind of assume you're going to do something with that frizzen spring too.
How about posting some progress shots here as you go along? I have no idea how you do half the stuff you do and it would be great to see things progress or in-process.