A molding arrangement is provided for multi-level stack molds wherein mold sets and runners are made up of modular sections interchangeable individually or as larger assemblies for exchanging molds for one part for those for different parts or exchanging runners between hot tip and valve gate designs to accommodate different molding arrangements. The arrangement has discrete melt paths for each mold level, at least some of which extend around rather than through the mold levels and which incorporate readily separable connectors. This enables one set of molds and possibly as well the runners for one mold level to be interchanged without interfering with the mold and runner arrangement for an adjacent level.