I finally got around to opening up the XPD-1LR pad, and I've put it up on the wiki:
http://gamesx.com/wiki/doku.php?id=controls:x68crazyclimber
This is the dual D-pad released with Crazy Climber, which also works with Libble Rabble.
It's a really cool system: One 74157 (http://gamesx.com/wiki/doku.php?id=chips:74157) chip switches between the two d-pads as required. Games that don't toggle the OUT line of the controller port would simply get one pad, so it would work fine on all normal games (the two buttons are not encoded through the chip).
Check it out. =) (http://gamesx.com/wiki/doku.php?id=controls:x68crazyclimber)
That 74157 chip is everywhere!
It's almost the 555 of the controller world.