[21 v] He isn’t [enough of a scholar]. (CGEL, p.534-5)
In construction [v], scholar is not head of the whole NP but part of the of phrase complement, and for this reason it must follow enough.
They are, it seems, saying ‘enough’ is a noun, but I’ve not yet found the proper nominal meaning of ‘enough.’ Is ‘enough’ a noun there? What does it mean in [21 v]?