Originally Posted by Phantom Power
The difference is on the diameter and threading of the part of the pump guide rod that threads into the front of the body. Where the front block banjo bolt usually goes on an Autococker.
While I suppose technically it's possible to turn down a 2k bolt and rethread it (since it's larger in diameter than the 99), it would probably be easier just to sell that kit and buy the one you want.
Actually, drilling & tapping a pre-2k body to take a 2k+ pump guide is a whole lot easier than modding the pump guide.