if your tring to put an 8" V6 third into an IFS housing, it won't fit. the V6 third will bolt right into your rear axle housing though.
as you stated the V6 is an 8" gear set, the IFS is a 7¢" gear set. they are not interchangable.
now if you have a solid front axle(SAS) then the third will bolt right in no problem...........Karl