What MSD box for timing retard when using nitrous?

The titles say it all. I'm going to be running a nitrous kit soon. I'd like to switch up to a MSD ignition box before I do so and just in case I go with a dry kit over a wet and need to retard timing (I don't want to have to do it at the distributor every time) What would I need. Thanks.
- Justin

My mad searching skills yielded this. So here's a link for anyone that finds my useless duplicate thread.

http://forums.stangnet.com/showthread.php?t=701087&highlight=nitrous+wet+kit

Sorry to start another unneeded thread If you do have additional input though, it is appreciated.