rear end

[John Z]

This is a good question that I haven't seen good documentation on rearends. I think that Gearhead is correct. The 8" was the primary rearend for v8 mustangs, with the 9" reserved for special orders and hipo cars. I6 cars came standard with a smaller rearend, either a 7 or 7.5", not sure which. The 8.8 rearend is a "relatively modern" rearend, definitely not in a classic. Here is a page that gives some info on rearend ratio's that were available. Unfortunately it is not year specific. If the tag is still in on the rearend you can figure out what ratio came from the factory. http://www.ridgenet.net/~biesiade/Fordrears.html
I believe (would not bet) that the "standard" rear ratio for a 289 C code auto was 2.73 and the manual was 3.03.