In an aspect, a mold stack may comprise two adjacent components, one at least partially defining a vent adjustable between a molding configuration and a cleaning configuration. A junction of the components may be adjustable between a molding configuration, wherein mating faces contact one another to define a parting line, and a cleaning configuration, wherein mating faces are separated to create a molding cavity extension therebetween and an auxiliary melt barrier prevents uncontrolled flashing from the extension. In another aspect, a mold shut height adjustment mechanism may include a mold component movable along an operational axis of the mold, a stop member, movable along the axis relative to the mold component, having first and second stops for providing first and second gaps on the front and back sides, respectively, of the mold component when the stop member is deployed, and a spacer for use in selectively deploying the stop member.