I've just realised that the idea of IR-OPS was to be less restrictive than EU-OPS in some areas with the difference coverd by 'Acceptable Means of Compliance' or 'AMC' guidance (also know as 'soft law' as these documents are not written into the regulations).
I've just had a look at 'Acceptable Means of Compliance (AMC) and Guidance Material (GM) to Part-CAT' and found it all there.
Interesting stuff I know.
Thanks for the help!