yes you are correct. the 3 series carrier is for 3.07 to 3.5? gears.(they only used 3.07's 3.73's and 4.11's in our trucks) the 4 series carrier is for 3.73 and up gears. here's the way to tell the difference. just take these measurements.
doesn't matter if they are open or posi.
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1969 C-10 292 I-6 4 spd in the middle of a restoration. going to get a 327 and 3.07 gears but keeping all of the original parts so I can put it back to original later on down the road.
55 chevy 4 door 150
47 Willys CJ-2A
[This message has been edited by texnician01 (edited May 15, 2002).]