There is an interesting page on another site by author "LESchwartz", titled:
"The Ultimate Removable SKS Mount"
ht tp://www.sksboards.com/smf/index.php?topic=85926.0
This is an excellent "how-to" article on adding a "full rail" to an SKS, extensively illustrated, and described step-by-step.
The idea is similar to the Top Rail mounts for the CZ-858, developed independently by DMcFaul and Kasat and written up in Curtton's CZ-858 Optics, Sights & Mounts sticky [f.TOP RAIL MOUNT] - put a full length of picatinny rail between the rear dust cover and the rear iron sight mounting.
The front end of the picatinny rail is pinned to the rear sight mounting by a bolt. The rear end of the rail is attached to the top of the dust cover with screws and tapped holes (aided by a layer of J-B Weld between the picatinny rail and the dust cover). The rear takedown pin of the dust cover is removed and both sides of the receiver, as well as the dust cover rear block, are tapped for a cross bolt that threads through all three.
Both the front and rear ends of the picatinny rail require milling (or grindng and filing, for those of us without milling machines) in order to achieve a close fit at the mounting points. However, no "gunsmithing" as such is required. The dust cover that is drilled and tapped is a replacement such as can be purchased from any number of suppliers (NcStar, Leapers, Fitco, etc.), and the only permanent physical change to the rifle is the tapping of the hole for the dust cover takedown latch pin. This step could be omitted if the builder didn't want to permanently alter the rifle. The issue of return to zero is discussed at length, and the reason for tapping the receiver and dust cover takedown pin hole is explained.
Mine is under construction - slowly. I am also considering the Weaver Convert-a-Mount option which, although not "full rail" gives a wide variety of choices in size and type of optic to be mounted. It's also remarkably inexpensive.
For the full story on these and other options, check out Curtton's SKS sights and optics sticky at the top of this forum. Many contributions and many different ideas have gone into making it a superb reference document.
http://www.canadiangunnutz.com/forum/showthread.php?t=439418