Ben,
If you recall, I posted my idea of what your block would look like in the "Ultimate block? Theory" thread. Since then I've come up with a few ideas, which I will post, if you like. A couple of q's come to mind:
1. Have you given up the idea of the fins at the bottom imparting a "swirl"? ie. curved vs. straight radial fins.
2. Are you wedded to the idea of a uniform thickness baseplate? Recall that Cathar's fins brace the baseplate against the cover, effectively giving him a stiffer bp to compensate for his lack of thickness. Also, his has a higher density of "finnage" than yours will at a given point, I believe. Refer to my posts in the "Ultimate waterblock" for the direction I am heading.
As to Cathar's block, I believe he said that he had the fins EDM'd into the copper. When I talked to one of my co-workers about machining 1mm channels into copper, he wasn't particularly enthusiastic. PITA!
I also have an idea or two re: mounting. If you prefer, I can contact you off-line, but that might be considered bad form. In any case, any help I might be able to give re: CAD and NC Programming is available.
Bob