Hey cathar, I'm a little late to discussion, but I follow your progress. I am thinking of ways to make thiner fins and thiner chanells, maybe even base,and now I finaly got some idea how to make even thiner chanells on my mill, but I need to test this first before making a fool from myself
Anyway the thing with thiner fins and chanells is the the top and how it's designed , I see in your block that the top covers the fins and is basicaly touching them, no problem here if ID of the inlet measures the total width of all chanells and fins, all the chanell are in contact with water flow. But when you test with nozzle like inlet and if you had the same top with no or just very little distance between nozzle discharge those outer chanells won't be realy exposed to water jet. So some rounded cut out on the top, just above the core with nozzle in the centre covering the fins would be better.