3.73 carriers are not same as 3.07 carriers, the split is from 3.40 to 3.73
2.76-3.40 use series 3 and 3.73-4.88 use series 4
the difference is in the mounting flange for the ring gear where its located from one or the other end of the carrier, they are about 1/2" differnce from 3 to 4 series, IE the ring gears for series 4 are way thinner than for series 3 because of how small diameter the series 4 pinion gears are, they tried to fix some of it by moving the ring gear mounting surface on the 4 carriers over to compensate for that to a degree, you can tell the difference between both series with a tape measure. series 4 carrier gear mounting flange is 5" away from the outside edge of bearing thats pressed on to the end of the carrier farthest away from it.
series 3 wil be about 5.5" distance.
go to randysringandpinion tech section to learn why and how this works.
personally i have yet to see a truck 12 bolt that has 3.08, always use 3.07 from what ive always seen,
the 8.5" 10 bolts maybe used 3.08 however