One of the easy ways to tell the difference is look down behind where the engine bolts to the transmission, about 6 or so inches below where the distributor goes, the 904 has a pronounced ''wrinkle'' on the outside of the case where the top tapered part meets the bottom horizontal gearset part, and the 727 is smooth. The 904 kinda looks like it was dropped on end when the aluminum was still hot if you can imagine that. The 727 is markedly larger than the 904 including the pan.The tail shaft is longer on a 727 too. These are just at a glance visuals.
Someone will come up with pictures i'm sure......
