i always thought it was the 2.5ish offset, like the dana 60 and 8 3/4" ?
looking up the dakota drum to try to compare it with the earlier 9 1/4" rear used in other model pickups, i could only find 6 bolt drums, so i don't know if the offset is the same between the 5 bolt axles and the 6 bolt ones.
i know member poorboy will know for sure, as he is the dakota expert here.