I looked and when I called GAP a year or so ago, they weren't interested in doing that. I could have bought their rifle and just put the stock and handguard on it had I wanted. I looked at others too, some not KAC or KAC types. Ended up going with KAC, got an SR25 20" rifle w/keymod tube and QD suppressor mount. I also got the suppressor that mounts to it. This is the new rifle anyway, the military versions are the same except they have a Magpul stock and the more expensive brake mount.
Now the KAC rifle is a different beast. The gas block doesn't fit or work like a normal AR type and the lower is fully ambi with built in left and right mag and bolt releases where they should be. So you can only build on so close.
For the price, why not just buy a 16" KAC rifle and then if you must have that stock and tube, just put it on? I mean, if you already have it, you wouldn't be out any extra save the rifle. If you must have the long can (which isn't as good as the new QD can) then you can always get the right flash hider and gas block to swap.
The SR25 is a fine rifle, I am absolutely satisfied with mine. Came with sights, extra rails, grip covers and some other parts. I got extra mags and the cleaning kit with extra parts; pricey but it is nice and with a few special parts added I felt it needed. The keymod tube even grew on me enough that I used it on a couple of builds. It's easy to use, one piece, solid and lighter too. Still, I got it all minus the can for less than $5k, but I also ordered a lot of extra stuff. The rifle alone could be had for $4k-ish, plus or minus.
Why go with a clone when you can have the real thing? I mean, it really is a damn fine rifle. Cut rifle barrels and that 2 stage trigger is fine enough I just left it. Give the SOPMOD and keymod a try before swapping out. You may like it. Good luck!
BTW, they still have the "old" military rifle... For $24,000 IIRC. But it does come in a case with drag bag, mags, parts, cleaning kit --all sorts of shit-- but doesn't include the can or clip ons for that price.