Has anyone done this with success? It doesn't look like a problem except for modifying the hand guard. It looks like there is plenty of material to work with. Below is a responce from Ultimak. The handguard on my rifle is not retained or efected by the gas tube.
"The handguard would need major modification, and on our Saiga, it would mean that the optic mount is now responsible for restraining the forward movement of the handguard. Our original Saiga gas tube has flanges on the sides in the back, which interface with slots in the handguard for front-to-back retention of the handguard. Installing the mount will defeat this feature, so the large cutout required to accommodate the mount will need to serve the same function. "