I am about to pick up a used diff tomorrow for pretty cheap however I wanted to know how are you able to tell the difference between it being an open or VLSD without pulling the cover? Do I just turn one of output shaft and if the other turns the same direction then it has VLSD, or do I turn the main shaft and see if both output shafts turn the same direction? Also is there any visual differences between the output flanges?

Last question, for the 6sp differentials, the input shaft is 4 bolt flange vs an automatic is 3 bolts flange correct?