Given my somewhat obsessive interest in sights, and the lack of the photo to be forthcoming, I'm going to hazard a guess your "non original blade" (the top of which shows in the (disassembled) photo) is a Lyman #19 (also known as an "ivory slide" sight). Now, truth be known, that's a fairly simple deduction in view of the fact the upper portion of the Lyman blade is considerably thicker than the S&W blade (as is the blade shown in the photo)---and the fact that there were only two commercially available blades that will fit your base---S&W and Lyman. As to whether it's original or not, a letter might tell you---and might not---as it was available as an option. I'll hazard another guess, and agree it's not original; simply because they were normally fitted in conjunction with a Lyman ivory bead front (#16)----which yours is not. The remaining choice is the rear's original, and the front is a replacement. The acid test of my guess is the appearance of the rear blade----it should have an ivory bar on either side of the notch---the proper sight picture being the front bead centered in the notch and in line with the rear bars---one of, if not THE first of the "three dot" sights.

Ralph Tremaine