It's what I'd do in your shoes
. My 'ideal' version would be a radial pin block made from a cross cut TT 1U P4 HSF, it would be very low profile...
I would try to work out the area of waterspace between the fins (seen 'end on') to make it slightly less than diametre of the tube feeding the block, so I can work out how high to make the fins without making a pressure drop in the block...
BB2K can probably help you out on the 'jet'/orrofice dimensions, what the ideal depth would be (thickness of 'jet' plate). There's an 'ideal' max lenght I believe?, where going past it is'nt benificial?...
PS, you could make everything but the T/T base plate out of Lexan if you wanted...