Had to take one of those half circle woodchisels to carve the channel to fit the barrel into the thing, was a good deal of work, but it fits.
Other points to note is that you will need to drill the center screwhole in the stock a bit more deeply, as the stock retaining screw there isn't long enough. About a CM or two in depth and that should be fine.
There is also a protrusion on the back of the receiver which is another retaining point for the tactical stock that comes with the gun. You can either remove that entirely, or cut in a slot in the stock to fit it in place. Once set in the stock itself, you don't have to worry about tapping or drilling a hole in that for the screw to fit into. The one in the bottom center is fine.