Nice specimen. It's still one of the "old style" with the cast trigger guard, i.e., the über cool version. How does it shoot?
I would imagine your backstrap is drilled for a Lyman No. 43 or 44 sight. I don't know the thread size offhand, but you ought to measure it with a wood match and a thread gauge in any case. Your gunsmith ought to have plug screws to fill the holes. You may find a replacement silencer before you luck onto one of the sights.