A store near me has a case of conversion kits to convert Czech she rifles in 7.62x45 to 7.62x39.
They include the chamber adapter, some locktite and a headspace guage/insert seating tool thingy.
They want $20 each for the kits.
They are Summit Ammo, and the # is 1-877-726-4345.
BTW, I am not affiliated with them, it just seemed like a good deal.