Please don't forget that Ultimak is will not fit Yugo AK47 rifle (modifications will be needed).
1. The differece between reguler AKMs and Yugo AKMs is that Yugo's gas port is located 1/2 further from the trunnion than a reguler AKM.
2. The way Yugo's gas tube locks in the rear sight base is also little different, so Ultimak will not lock in there either.
So the only place Ultimak will be able to lock in properly is the two clams on the barrel, which probebly will not hold is stable because you will be using 1 instead of 3 mounting points.
I explained this in the post a few days back, no one seems to believe me. So in the case you do try it please take a picture and do a review of how it will work.
I tried to mount an ultimak on my Yugo and after seeing how loose it is I sold it.
Since than the only best place to mount optics is the side rail. But for underfolders the side rail has to be much thicker than for full stock AKs (because the underfolder button will be on the way of mount any optics on the rail.)