10 vane water pump for 273

I have done a LOT of experimenting with water pumps. As far as the cause of o'heating, there is something faaaar more important than the number of impeller blades, their shape or their size. It is how well they fit in the cavity they reside in. If there are large gaps around the impeller, the water has an escape route; it just gets churned up/recycled, but is not captured & pumped through the engine. I have often welded a 'donut' onto open impeller blades to capture the coolant & it gives a noticeable reduction in temp.
This might not be feasible with all pumps, but something to look at/check out.