A little update here is warranted, I suppose.
I bought the student version of SolidWorks (for a pittance!) and have spent a few hours fooling around with it. I've decided to optimize the arrangements for a lower restriction pin block and to also design a block that performs on entirely different principles (for a pin grid block, anyway).
Following Ben's advice, I buzzed a couple local machinists about their capabilities, and was told, essentially, that if I could supply a slitting saw, they could cut the copper. After finding .0080" and .010" (.254mm) solid carbide saws (with reasonable +/- .015 variances), I'd figure I'd try and design for the latter. The result is 612 diamond pins .6mm x .4mm with a height of 3.7mm (effective cooling patch is 1.9cm x 1.2cm - a little on the small side with respect to width).
Debating my choice of material and baseplate thickness for this one - I'll likely reduce BP thickness to somewhere around 1.7mm to 1.8mm in the hopes that edge chamfering will give it enough structural rigidity. May also implement G7-style braces on the midplate to help keep things as evenly flat under loads as possible.
On the subject of the lower restriction prototype I have in the pipeline, I'll be rethinking some of the priciciples in hopes that I'll be able to reduce crossflow and stagnant flow regions. Something of a microcup+pin configuration. More on that later.
I'm still collecting items for the testbed. I intend to pop the IHS on my old Intel 2.4C, probe it and power the loop with an RD30, though searches for the RD30 have proven to be feeble. If anyone has any leads on these things, I'm all ears.