A non-dimensional physiology lacks the very properties of a dimensional thing, so something that is non-dimensional purely due to it's superiority over dimensionality is 1-A. So the Afterlife which "transcends dimensions", would be on the "superiority" bit and not the "alienness" bit, the problem then lies in what dimensions in this context means.
Dimensions, as repeatedly used in both daizenshuu and Dragon Ball is a reference to realms and universes, however, if we assume dimensions here to be a reference to dimensionality as a whole, then the Afterlife would transcend them, and would definitely have no dimensional property. So it's between Low 1-C and 1-A, you can't really get any lower with a statement like that.
There is another translation however, that claims a superiority over dimensionality as a whole, which would obviously leave no room for interpretation and be a clear cut case of qualitative superiority, thus 1-A.