I am an experienced engine builder, but I just inherited a 1978 Nordic jet boat. Very cool, but nobody on the East coast knows anything about them. The boat was set up for a big-block Chevy, and I have installed a stout small block in it's place. I bought the proper hub to connect to the Berkeley 12JG drive and installed a pressure relief valve. The thermostat housing is of course different than drag race engines. There  is a small plastic or rubber impeller with a spring. Do I need this-where can I buy one, and does the spring go on top or below the impeller? Thanks much.