Fresh water / closed cooling system conversion

I would like to convert my original twin 427s to closed cooling. Does anyone know whether any of the kits I am able to locate online will work, or do I need something specific?

It looks as though you could just buy the heat-exchangers, the overflow tanks, and the hoses and clamps, and an electric extra raw water pump (since the current mechanical one would become the closed system-pump) and set it up yourself based on the diagrams from the Commander site.

Am I missing anything?

Advice needed.