rear end style question

[71GTKammback]

I have seen many 6.5" early Vega rear ends. 4 link. No panhard bar or torque arm bolt holes on the diffrrential case. The 7.5" later monza vega had the panhard and torque arm. I am looking at one that has code DC which decodes at a 75 6.5". 4 link but it has bolts for a torque arm. Why would it have 4 link and torque arm?