REAR END help!!?

how can i figure out wat size rear end is on my duster? . .it has markings on it like it came from a junk yard before i bought the car. so i dont know how to tell wat it is?? i want to change rearends as well. . .im going for alot of horse power and i know i need a rear end that can hold the power im trying to dish out between 400 and 500 hp. so what should i use. . i seen a guy use a dana 60?? is that a good choice or dana 40? or any other diffs out there. . . i dont know much about diffs thats why im asking??. . and if i was to put on say a dana 60. . could i pull one off a pick up truck and throw it on or wat. . . . your help is appriciated thanks!!!!