How about an AR-15 with the 4 position CAR stock, a 14.5 inch barrel, with a perminetly attached flash suppressor bringing it out to legallength under Federal law?....
As for the AK's no no stock spacers for AK's, and if the slant break isn't long enough then theres a few options, 1 get a spetialy redisighned break that brings it out to legal length but still looks like the origional, 2 put the origional on loosly so it's still out to legal length and pin it like that, 3 weld a small steel pin to the front of the break so that the end of the pin is out to legal length, 4 fold the stock then weld a pin to the back of the stock, or back of the reciever so that the total length when folded is still legal, 5 use an AK-74 break, if your going for correctness just build an AK-74 to begin with....