Update 2

One potential concern with this D-Sub Adapter is the small traces in the PCB.

As another option, you could just use the Cobra Slat Adapter connector. These were purpose build with high quality parts (probably gold plated/flashed connectors) and very nice large traces. To use these, you'll need to remove the cues 13-18. I found breaking the plastic connector, then using a pliers to pull on the wire from the connector while applying heat from a solder gun to the back side pins would release them nicely.

Here's what it looks like with the cues removed. See how much larger those traces are (the things that connect the pins within the board).

To attach one of these to the Seahorse case, I swapped out the middle nut with a nylon spacer. I had to file it down a bit on one side to get it close as mine were a bit larger than the nut. I chose to do this since I wouldn't be able to get a tool to that nut when it was being attached to the Seahorse case. The nut on the back side should be fine. (Worst case you could apply a little glue to it after tightning.)

It needs to sit flush against the inside of the case. You'll need to chisel/file away a bit of the excess plastic under that middle screw support as seen in the above picture.

Here's what it looks like installed.

It should be easier to wire as well. The 3 bundles of 7 wires should plug directly into the 21 pins of this adapter. (As opposed to pulling out the grounds from the 25 pins of the other adapter.)

The standard or the Left exit slat adapter should work equally well. The one pictured above is the standard.

The Left exiting slat adapters are sold on the Cobra Accessories page at http://www.cobrafiringsystems.com/index.php?route=product/product&path=60&product_id=198

They are currently $9.95.

Continue to Update 3