What you have to do is fit the forend into the forend retainer until the crossbolt falls into place.
Then, you will probably find that the barreled action is slightly cantilevered (has to be that way) in order to get a good tight fit before the tang clip falls
into it's notch in the trigger guard.
I had to remove material on the stock where the little spring goes with a rotary tool & bit.
By the way the stock is in there so tight & cantileverered that this spring is un-necessary.
Edit:
what you have to realize is that the forend is made long on the red chinese stocks to allow you to fit it into your sks.
also, the action mortise on the stock leaves 2 kind of weak / floppy sides in this area, but this is only when you are examining the stock apart from the barrelled action.
When you finally fit the forend such that the crossbolt finally drops in to where it has to go, you will find that the rear of the action is cantilevered from the crossbolt area to the rear of the receiver.
The reason for this is to put tension on the part of the stock between the crossbolt and the rear of the receiver.
Fitting:
you will have to start reshaping and filing the front face from, the stock forend.
As you do this, the rear of the receiver is going to fit closer and closer to the extreme rear of the stock mortise cut.
This means as you file more and more off of the forend tip, you are going to have to correspondingly file more off of the rear stock mortise.
This is a slow and painstaking process, plan on installing/removing the stock about 50 times or so.
When the crossbolt finally drops in, you now have to change focus on the seat area for the rear of the trigger assembly.
On the original SKS stocks, and on the red chinese phenolic ones, there is a blind hole for a spring that applies downward pressure on the trigger assembly.
Because a significant amount of pressure is required to get the receiver tang clip to engage into the trigger assembly, this spring is not really required.
Also, as wood may move depending on the climate conditions, the red phenolic stock is not going to move whatsoever.
But I digress, you are also likely going to have to fit the trigger group into the flat area in the stock for it around the blind hole for the spring.
This is best accomplished through use of your rotary tool with the 'end mill' type bit. Be careful - don't even think of filing on the trigger group as the milsurp gods will smite you.
Tools needed:
A good rotary tool with an: 'end mill' type bit,and a little sanding drum as well for it.
a pillar file with 3/8" X 3/8" square profile, or even a 3/8x3/8" square profile wood stick with sandpaper on it.
A bastard file about 8-10" long.
Maybe a brass drift and a hard plastic mallet to encourage the trigger group to engage the receiver tang clip.
A gunsmithing vise would be nice, but not entirely necessary - you can make do with a good sized wood block to rest the top rear of the receiver on while pressing the trigger group into position.
You should be bloody tired by now with a cool looking all-weather SKS.
