What you have is a Chinese Type 56 SKS variant set in an ATI/Combat Exchange Monte Carlo stock. Can't tell from the pics but it looks like it is a post ban with the Bayonet lug filed off, but that could be an illusion on my part. Anyway, only the Yugo M59/66 has the gas valve you are referring to. The valve is so you can shut off the gas system in order to operate the grenade launcher that is an integral part of the M59/66 rifle. No other SKS variant has that feature.
As for your gas tube release lever DO NOT pry the lever outward yet. A lot of times with aftermarket stocks there can be a binding between the lower stock and the hand guard. Tapco T-6 stocks are notorious for this. When that happens, if you install the main stock body first and then the gas tube, the binding at the HG will not allow the gas tube to seat properly at the rear thus causing the problem you are having with not being able to push the lever all the way down. This is what I would do as a process of elimination;
1. Remove the stock body then try and install the gas tube first. If the lever closes completely then that is your problem for sure. At this you can either just remember to install the tube first on re-assembly or file on the HG where it is binding against the stock in order to give some pressure relief.
2. If the gas tube locking lever still won't seat all the way it could be that the aftermarket HG has caused a shift in the position of the rear ferrule which is causing the end of the tube to bind against the lever cam at the front of the rear sight base. If this is the case then just a little filing on the angle of the tube at that point should give the required relief for it to fully seat. If this is what you end up doing remember that a little is a lot when dealing with firearms tolerances. Accordingly, take 1-3 swipes with a fine bastard file or diamond file then recheck for fit.
Hope that helps
Last edited by greatguns; 07-14-2011 at 01:42 PM.
If if's and but's were candy and nuts we'd all have a merry christmas.