are you going to do something like the 7i37? There is board design on Anders Wallin's web site.
I am trying to get my mill set up with a Mesa right now. There is a lot of work to do, almost none of it involving the Mesa board. I am working on the estop and limit circuits, which are fairly important when you have hundreds of pounds of metal sliding around at high speeds. I'm afraid to test my wiring until then. I stumbled upon some 50 pin ribbon cable to screw terminal boards, which makes things easier with the mesa. I did have some problems with packaging the breakout boards. They are inside the computer now.
I have a couple of the BD23a20's, but I decided to use different drives. Not that it makes much difference. In my case, the encoder wiring goes through the drives. I do have the drives wired to the mesa. I got a spreadsheet from someone on the emc irc channel and modified that.
I'm posting it in open office format