differences in 727 transmissions

Can someone explain to me the difference in some of the 727 transmissions? like is one out of a truck the same as one out of a car? what kind of cars are good donors to find these in? and if i find one how will i know if it will fit in my car, like if it has the right tail housing and what not? looking for one to put in my 71 scamp behind a 5.7 hemi so i at least know it needs the small block bell housing.