it looks like you need a plate with a manifold in it. Kinda like my gpu block but I make mine with 1 plate because of the side enterance.
Basicly cut it out like you have it. but at the ends, make 1/16" or 3/32" slits that go all the way thru, and mill down so its really thin area like that, with a 3/8 end mill so theres area for the water to go side to side.
sorry, my dad took my digital camera on a motorcycle trip, so I had to use the cheap webcam.
basicly make one plate that looks like that with the botttom milled out for the fins, then make the top with the hosebarbs in it, and a slot for water to travel to the ends of it easily. Neither the way you have it and the way I told you will flow perfectly, but I beleve mine will flow more decently with lots more flow.
Thats the first pic of my gpu manifold on the web
Jon