Jeff,The rifles(Zkk and Cz) are pretty much the same so it would be a case of fitting a slightly longer action stock (CZ550) to the slightly shorter rifle (Zkk601) .I do not own a ZKK 601 but I do believe it is slightly smaller between the screws than a ZKK600. A Zkk 600 and a CZ550 are exactly the same dimensions .In this case it could be done but it would take a little work and some stock inletting and bedding skills.