A mold for use in a gas-assisted injection molding system includes an adjustable overflow pin assembly which includes a conical stack of shims which are removably secured to an ejector pin to move therewith within a conically-shaped spill cavity flow-coupled by a secondary runner to an article-defining cavity of the mold. The mold also includes a blocking pin assembly which together with the adjustable overflow pin assembly are mounted on an ejector plate to move therewith between extended and retracted positions of the ejector plate. The blocking pin assembly includes a blocking pin which is slidably fit within the second mold half to move relative to the ejector plate between an extended blocking position to block the flow of molten plastic through the secondary runner and a retracted position to allow the flow of molten plastic through the secondary runner and into the spill cavity. The blocking pin assembly includes a hydraulic cylinder for slidably mounting and moving the blocking pin relative to the ejector plate. The blocking pin has an end surface which partially defines the secondary runner in its retracted position and which partially defines the article-defining cavity in its extended blocking position. The adjustable overflow pin assembly and the blocking pin assembly, as well as other ejector pins mounted on the ejector plate, eject plastic from the article-defining cavity, the spill cavity, and the secondary runner in the extended position of the ejector plate.