Just to add in from my experience on adding a crane stock to an ICS gun.
With a lot of searching online, and a lot of help from XavierMace, I pretty much got it down on how to put a crane stock on. I went out and bought the G&P crane stock kit with 9.6 battery, and began to file down my stock adapter. Finally, after destroying a $8.99 dremal, and some work with a file, I got the adapter to fit the tube.
Now theres only one problem. The instructions state that this is a newer tube, its hollowed out more so the walls are thinner allow for more room, and it has cut outs at the end of the tube that runs across the tube about half way (allows the stock to fully colapse with the G&P battery). The instructions also state to cut down the "stock adapter" (which on other brands its built into the reciever) and leave about 3cm left. Reason for that (if you've taken off a buffer tube you'll know what i'm talking about) there's a washer that you put inside the buffer tube, and a screw that you run through the washer and the screw reaches the stock adapter (or end of the reciever on other brands). The washer slides into the tube and stops near the middle of the tube, where the tube walls are thicker, thus mounting the buffer tube onto your gun and holding it into place. Now if you cut the "stock adapter" on like a CA M15, thats fine, because the whole piece is normally solid and the screw threading runs throughout this "stock adapter". On the stock adapter of the ICS gun the stock adapter is hollow and only the end cap has screw threading, so if you cut the adapter off, you'll have no where to screw into. On this G&P crane stock buffer tube, the part where the tube is thicker for the washer and screw to catch is located near the bottom of the tube, about 2 and a half centimeters away from the reciever when mounted. So when you insert the stock adapter into the buffer tube, it actually extends into the tube further than the thick part of the tube, so how the washer that you will insert will never reach this point, hitting your stock adapter.
So beware of this G&P buffer tube and other tubes like it. Just make sure when the stock adapter does fit, that it doesn't extend past the "thicker" part of the buffer tube, cause if it does, you really have no way of mounting your buffer tube on, unless you get creative, gluing it on, welding it or some major fabrication. XavierMace also pointed out that a thing QD Sling mount, that is thick enough would extend your tube out more, but giving you the clearance for the washer and screw to hit the thicker part of the tube to mount on.
I ending up purchasing a king arms buffer tube, which thank god fit my G&P crane stock perfectly!
So ya, the G&P Crane kit is tempting cause it comes with everything you need and is a good price, but the buffer tube really doesn't work unless you put some "crazy" work into it. Your better off finding another buffer tube.