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
only a 255 pnd difference? i would think its more than that, course theres so many differnt ranger weights. a shortbox 2wd vs a 4wd s/c would be alot. final drive gearing does alot. dont know what ratio a taurus uses, i wouldnt have less than 3.73s in a ranger chassis, and preferably 4.10s with the 3.0 remember the 3.0 makes its power higher in the rpm band than the other motors available. its a good motor, definitly a upgrade from the 2.3 but the 4.0 has more power at a lower rpm and isnt much differnt on fuel economy, unfortunatly the 3.0 and 4.0 have differnt bell housing patterns and cant be exchanged for each other without a trans change, otherwise id put my higer-milage 4.0 in the wifes lightweight taurus (just to bump up the performance a bit) and give the ranger a low-milage (only 60,000) engine. then id change my gearing to make up for the power difference. but, not possible so just a daydream. the taurus is a tire-fryer by the way.