that is an interesting number - I don't know if I have ever comeacross unique (Pontiac application) California carbs other than ones from the 1970 model year - yet the initial application suggested was exactly what my guess was;
70 = series
4 = post-1969
4 = 1974
5 = California emissions (the normal is a "2")
6 = Pontiac (6&7 were Pontiac numbers)
0 = even number denoting automatic application