Clearly 91.179 (b) is what applies to Class G and I don't see the problem, assuming the word "turning" is the same as "manoeuvering" which is what one does when landing.
I agree that on a strict reading one probably gets better privileges for a DIY IAP with an IMCR (in a G or N) than with an IR in an N-reg.
The IMCR should be valid in an N-reg (I have checked with both the CAA and the FAA) and additionally the FAA permits the exercise of foreign license privileges (FAR 61.3). So the full privileges of an IMCR should work in an N-reg. But we've been around this one before
The practical question is how low would you go on a DIY IAP anyway? 1000ft is a reasonable MDH. I know lots of people go lower, especially using the unpublished IAPs which exist at various UK airfields; sometimes these were real IAPs at one stage and were "lost" when ATC left, others are approved only for use by based commercial ops. Most have been CAA-surveyed.