The FAA's published Swift fuel tests contain good detonation data for two engines, one of which is the TIO-540-J2BD, the angle valve turbo six from the Chieftain. None of the test points pull RPM into the 1800's, but it should be much the same combustion chamber. The closest test point is 2200 RPM and about 33" manifold pressure.
There does appear to be an interesting trend, in that detonation onset progressively moves toward leaner mixtures as RPM is reduced.
At 2575 and 42", detonation onset is found at the classic position, ROP, just leaner than best power mixture. With each power reduction it moves to a leaner position, with 2200/33" being slightly LOP.
Is it really relevant to an NA IO-360? I dunno, but I do note the manifold air temperature, 161F, well above the 100F standard I think is used for detonation certification with NA engines.
If you get curious about margin, push mixture richer from your very lean setting and watch the CHT trend. If the rise shows a knee, you're tickling the dragon, but light detonation won't hurt it.