how to ID gears & spline on 73

Got a rookie question. How can I identify what stock gears came in my 73 swinger 318 as well as the the spline (I believe it may be 27) without opening the case? Looks like the factory installed either 2:45/1 or the 2:74/1 but the 2:74/1 would have been a factory option. is there a code on the build sheet or fender tag or diff case that would help me to clarify?