Answered By: Michael Cullen Last Updated: Sep 11, 2017 Views: 265
AGLC3 seems to provide no guidance on whether Roman numerals can be used as a pinpoint (page) reference in the way that you have, although the alternative of substituting '20' for 'xx' in your footnote would seem to be misleading.
AGLC3 1.1.5 Pinpoint References:
A pinpoint reference to a page should appear as a number...
AGLC3 1.4.2 Above and Below:
You seem to have complied with the citation rule, unless referring to one of the excluded resource types that are nominated there.