ever hear of a 2 series posi ?

[fnoblitt]

i have a 69 c10 with a 12 bolt rear and 3.73 gears (no posi).i'd like to change the gears to a 2.76 ratio,but i'm told they won't fit on my carrier because it is for 3.73 and up ratios. my question is,will a 2.76 ratio fit on a 3 series carrier,or do i have to find a 2 series carrier? does anyone have a nice used carrier or posi unit that this ratio will fit?

[Fast68Chevy]

2.73-3.40 are series 3

3.73-lower ratio/higher numerical are series 4