It depends on the years & models of Ranger & Taurus you're talking about. I put a 1996 Taurus 3.0 into a 1991 Ranger and it runs like a champ. For the most part, it's the head gasket and some very minor differences in the heads. If you're swapping the entire motor (long block) then it's a non-issue. Otherwise you have to do some checking to make sure you use the right gaskets. Check this site for more info on the "Vulcan" 3.0:
http://rogueperformance.com/WelcometoFredland.html