posi carrier
 

Will a 69 camaro 12 bolt carrier go right in to a 66 chevelle 12 bolt housing i thought all 65-70 carriers where the same ?

Yes

There is a 2 series, 3 series and a 4 series differential for the car 12 bolt. All will fit in any car housing, but they must be correct for the gear ratio that is being used. For example, you can not use a 4 series differential with a 3.31 gear.