Gonzalo, I would recommend an inline water pump. I have seen some folks run the Davies-Craig pumps but I have no personal experience with them.
I don't know if you are running a dynamo or an alternator, so efficiency may be important. Also consider what happens to the water flow when the power is lost. You want a pump that will continue to allow flow and not block the coolant line when/if power is lost. I have also heard of a need to regulate the flow to ensure it is not excessive to need.
Cheers,
Mark
