Tranny ID

A904 is the lighter-duty of the two. Slant-six and small-block territory.

727 is the larger of the two. Mostly big-block territory but came behind everything from Slant-six on up at different times.

Since you are asking on the A-body board you probably have a 904 which is NOT a bad trans at all. It can be built strong and consumes less horsepower in the bargain. If it's any testament my '73 Sport has had who knows how many engines but still has the original 904 trans.

I think nearly the only A-body to get a 727 may have been 340 and 360 cars.