I have a SBR'ed stainless sidefolder. have had it almost 10 years. I went thru all of the various front sights until I found and purchased a true ac556 front sight. granted, its blued, but its real.
here's the problem (and if photobucket still worked, I'd post a picture).... the repro front sights are too short (unless there's been another batch come out recently). I found that out the hard way. couldnt ever get my sbr to sight in right. at one point, I had both a blued and a stainless repro. after I got my real ac556 front, I stacked them on the barrel and the problem was very clear, very quickly. I even had one of those fronts made by the guy that dovetailed in a pistol sight or whatever. further, I had an ultimak type heatshield that had a ar15 type front post screwed into it. literally, I've had everything I think. (to include GB's and a very short m1a style front sight/flash hider combo on another sidefolder).
I guess my point is this; the only sight that will truly work correctly, is a real ac556 front sight (or at least, that was my experience). and the term "rare as hens teeth" comes to mind....
some pics in this thread with a repro front sight:
http://www.perfectunion.com/vb/ruger-mini-14-mini-30/71025-sbr-sidefolder-w-suppressor-*videos*.html
ETA: direct from ruger you can buy some very similar ac556 looking flash hiders. but....you guessed it....they're shorter than the originals. (I have one now on my sbr)
something to keep in mind (if I remember correctly) is that the original ac556 flash hiders arent the same thread pitch as "standard". think they're 1/2x20 or something, versus the 1/2x28.
ETA 2: if you google "ac556 front sight" in the pictures, about the 8th pic is a closeup of a barrel with 3 sights stacked on it. that's mine. I actually posted it on here in 2013, but since its photobucket, the actual image isnt going to work, its just a 'ghost' on google search. but you can see what I'm talking about.