Abstract: A hydraulic valve stack for a work machine is disclosed. The hydraulic valve stack has a base with a first mounting surface and a second mounting surface. The base is connectable to the work machine and has at least one fluid passageway extending through the base from the first mounting surface to the second mounting surface. The hydraulic valve stack also has a permanent valve assembly configured to control a permanent function of the work machine and an optional valve assembly configured to control an optional function of the work machine. The permanent valve assembly is connectable to the first mounting surface of the base, while the optional valve assembly is connectable to the second mounting surface of the base. Each of the permanent and the optional valve assemblies have at least one fluid passageway in communication with the at least one fluid passageway of the base.