Upgrade your MKII pump with a 304 stainless steel replacement head. Stainless steel is more durable if you are attaching ball valves. Very occasionally the threads on the plastic head that comes standard on the MKII can break if you are using hard to close ball valves that apply a lot of torque. Stainless steel is very robust and will not break, is food grade, and well... stainless. 

Stainless Steel Pump Head for MKII Pump