318 cars have 8 1/4 diffs?

My '79 R/T has the 318/904 combo. Will it have a 8 1/4 with 3:21 ratio? Or did the only 360 cars have the 3:21 raito? If the 318 cars came with 8 1/4 diffs then I'm going for 3:55 upgrade. Thanks!