727 on a 360

A bit of a dilemma... I have a 1971 360 that's going in a Dart, and I have a 727 Torqueflite that I got from a buddy that SUPPOSEDLY has the correct torque converter for the 360 (to my understanding, the stock transmission that the Dart has with a 318 will **** the crank) I'm not sure what would qualify this tranny to match the 360; does anyone here know how I would go about figuring this out? Counting splines or looking for some sort of casting number perhaps? Any help would be much appreciated!

Steve