To me it looks like a combination of two modifiers: (adj noun) and (noun adj). Sometimes (for poetic reasons) adjectives are placed after the noun (this also happens with certain adjectives, such as elect in president elect). So here we have human face, which is further modified by a post-positioned adjective:
((human face) divine) => "divine human face"
I'm not very well-versed in either Blake or Milton, but from a linguistic point of view it does not look like a specific structure to me.
UPDATE: "Miltonic structure" seems to refer to the verse patterns, rather than grammar, see http://www.theodora.com/encyclopedia/s2/sonnet.html:
Hence this critic, like William Sharp, divides all English sonnets into four groups: (I) sonnets of Shakespearean structure; (2) sonnets of octave and sestet of Miltonic structure; (3) sonnets of contemporary structure, i.e. all sonnets on the Petrarchan model in which the metrical and intellectual "wave of flow and ebb" (as originally formulated by the present writer in a sonnet on the sonnet, which has appeared in most of the recent anthologies) is strictly observed, and in which, while the rhyme-arrangement of the octave is invariable, that of the sestet is free; (4) sonnets of miscellaneous structure.