A mold assembly for manufacturing concrete blocks that is adapted for use in a concrete block machine. The mold assembly includes a plurality of liner plates, each having a major surface, the liner plates configured such that the major surfaces form a mold cavity having a desired form, and wherein at least one of the liner plates is moveable. A gear drive assembly is selectively coupled to the at least one moveable liner plate and configured to move the at least one moveable liner plate toward and away from an interior of the mold cavity. A stabilizer assembly is operatively coupled to the gear drive assembly and is configured to support the gear drive assembly as it moves the at least one moveable liner plate.