What Posi unit will fit?

[new271]

Hey Guys,
Anyone know what vehicle posi unit will work in my carrier?I have a 71 chevy c10 ,swb, shortbed,307,3 speed,coil spring 12 bolt rear.I think that should be all the info.If you need more let me know.

Thanks
Mike

[Green Machine]

If you are keeping your current ring and pinion, you will need to get the gear ratio also. I'm goint to guess it would be a 3.07 ratio. Gear ratio determines whether you need a 3 series or 4 series posi carrier. I beleive the split is at 3.73, that is 3.73 and higher numerically like 4.11, 4.56 use the "4' series carrier, and the 3.42 and lower numeriacally like 3.07 use the "3" series carrier, someone correct me if I am wrong. That same type rear was used from mid 60's to late 70's in trucks , no car swap available IIRC.