Hum, actually I tossed out the mod to the top that I dreamed up. All I need on the top is the openings for the outlet, but I also need that nozzle, which is a 5/8" plug, 1/2" thick, where the opening is 1/4", but has a cross in the middle of it that's 1.5 mm wide.
That cross is going to have rounded corners, to match the cross in the copper base. By "rounded corners", I mean where the fins intersect, since the channel would be cut using the same endmill.
See what I mean?
[edit] In polycarbonate, of course, which I would send you.