Check the tag for sure - but all the standard trannies in cars with the 8" that I have had, used the 3.00
With stick probably a 3.00... For automatic most without A/C 2.79, with 3.00... Only way to know for sure is check tag...
My '73 Comet with an original 302 and 3 speed stick without AC had the 2.79 rear in it from the factory.
Lets not guess and look at the door jam sticker for the axel code. 1973 (Same for '71 - '77) 3 = 2.79 6 = 3.00 Micah