Have you messed with a William's Firesight yet?
You will certainly need that windage adjustment on the rear sight....possibly all of it to one side or the other. The design is kind of flawed in that in order to secure it, you tighten down on a screw, which pulls it to whichever side you elect to put the head on. I attempted to correct this by inserting rubber washers and/or O-rings...which somewhat worked, but ultimately would melt. I have also heard that the SKS heats up enough to melt the optical insert...and that they tend to fall out. I never got that far. I fired maybe one shot to see if I got lucky with the placement, when I didn't...it came off and lives in the parts drawer. I may hang on to it should I ever pick up an SKS that already has the windage adjusted to the extreme.
What sucks is you likely will lose the cool factor of easily being able to adjust windage, precisely vs. the front sight drum...making up for an inherently improperly positioned FIXED front sight. Essentially, you will lose about half of the adjustability, making up for that. If the gun already needed to be adjusted to the right or left, I would suggest threading the screw in from the side it needs to be adjusted to already...which will leave you a little more windage. This leads to the ugly gaping hole left on the opposite side of the FSB where the drum no longer is....it looks funky if you have to thread from the left...if you display them.
These could have been designed a bit better, but likely would have been about $25 more expensive as a result. Another issue I recall with them is that they don't fit necessarily all nationalities of FSB. The thickness of the blade either is too much or too little for the slot it goes into....too much, it won't go in at all...too little, its way too floppy to lightly secure...so you end up pulling it to the side as far as it will go...so it stays straight enough for the light to pass towards your eye.
I highly suggest installing when you are alone, so the expletives can fly without damaging someones ears or your reputation as a level headed man. Why will replace What in WTF...I assure you.
I cannot see these being even slightly worth using without an adjustable rear sight. The likelihood of it attaching securely coincidentally with where it actually needs to be are quite slim. I added the Firesight to a pre-existing SKS sporting a Williams peep rear, that was perfectly adjusted for a standard post, and red-loctited into place by a previous owner. I didn't feel like fussing with it...as the aesthetics of it bothered me anyway....so they both went.
YMMV...let us know if you have success, and how you did it...I like the concept, if it worked better.