I've seen this conversion once before, but I'm curious on how you are planning on handling this coversion. The one I saw actually had the Northstar mounted in the rear. I did a search on google and found this in case you just wanted to turn the motor under the hood and run a drive line to the rear.
Here's the site: http://members.tripod.com/~grannys/enginescadillac.html
And a quote from it:
Can be converted to RWD by using a 700R4 transmission from a 60 degree V-6 powered S-10 or Camaro and welding in a special pocket for the starter.
Sorry, I couldn't find anything about making it a rear motor/drive conversion, but I hope this helps a little.