1997 Chevy Blazer Rear Drums to Rear Discs

I have a question about converting from rear drums to rear discs. I did not want to change or 'upgrade' the vehicle. I was at all the local junkyards (needed to change the complete differential assembly and is cheaper to just put a whole new rear end in the truck). The question is: I now am putting in a rear end from a 2002 blazer-mine is a 1997. The 2002 has disc brakes. Mine had drum brakes. What has to be changed? Do I need to change the valve that controls the pressure to the front brakes and the back brakes (I cannot remember the name of that valve)? If yes, I cannot find that valve (I already looked)-can I just connect the brake line directly to the master cylinder for the back brakes or would it need to be regulated through a 'pressure valve'? Do I need to buy a new master cylinder? This is only for a truck for beating around the area carrying things and I really don't want to change anything unless it is absolutely necessary-but of course I don't want to have rear wheel crazy lock ups as well. Where I am located it is impossible to find any parts for the 2 trucks listed above (I could buy a master cylinder new-but not the other pressure valve) so changing the valve would be a big problem. Please advise me on this as switching the new differential assembly to drum brakes is also a possibility.
Thanks, Stranded somewhere where parts are impossible to find.
Ryan