I was wondering if it was possible to use a msd box with a stock 91 mercury distributor. The distributor says white red, and white for the wire hookup, and i didnt know if you could just swap the purple and green for white red, white.

Thank You!

You can, but all as you are doing is adding a multiple spark, unless you are turning above 6k and a higher compression the Thunderbolt ignition is a good set up. You could purchase the Daytona Sensor CD-1 kit and set your own curves and rpm limits, that includes a coil. That way you will still have the hall effect, pick-up. Let me know if I can help.

I appreciate the insight. Basically what I am looking to do is run a motor on a dyno stand and I do not have a extra thunderbolt setup, but I do have a couple MSD's laying around. I just didnt want to have to swap out the distributor to run it on the stand.

As far as the green and purple wires, which posts should I hook them onto?

I can't recall the wire hook-up. to add the msd box, you will still have to run the control module, either way. The distributor and msd box will not work on their own.