IIRC - Prior to 79, you could get a Pontiac 400 W72 or non-W72, and both were available in automatics or 4 speeds. Starting in 1979, if you had a Pontiac 400 it had a 4 speed and was a W72. The W72 was a slightly higher performing engine than the non- W72, 200 hp in 77 and 220 hp in 78. I'm not sure about 79.
Check out the W72 document put together by John Witzke that's available on this website.