2.56 open regular cast iron rear, least desirable of all and not from a Firebird 400 but a low hp automatic car. All 67 bird rear housings have both traction bar brackets regardless. Ram air cars got 3.90 nodular posi rears, standard ratio on a 400 4 speed non-ram air was 3.36. The 3.36, 3.55, and 3.90 when ordered with posi got you the nodular iron housing, forged axles, ad hd 4 pinion auburn posi.