Tuning For Detonation

RRR,
Your detonation problem is a great example of the useless dynamic compression #s people use to try & avoid detonation with high static CRs by using more cam. There are just way too many variables involved & at the end of the day it almost becomes a crap shoot...........
Two things that rarely get mentioned are engine load & A/F distribution[ rich & lean cylinders ], but big contributors to det.
The engine doesn't detonate when revved in neutral, does it? That is because there is no load on the engine. So how the engine is loaded with car weight & gearing is a factor.
A/F variations per cylinder. I used to run a 4 bbl intake on my engine; had different intakes & carbs, 9.98:1 CR, iron heads. I had to be careful with the timing curve, but even then on very hot days, I could get light throttle ping. I THEN changed to a IR intake, home made, running 4 downdraft 48 IDF Weber carbs. One throttle bore per cyl. With the 4bbl, I had to use 98 octane petrol. With the Webers, I have the dist locked at 35* & MVA adds 13* for 48* at idle. Engine runs happily on 91 octane & I have never been able to get it ping. Such is the difference A/F distribution makes.
The inline 6 engine with a single carb is a particular problem because the end cyls with the long runners are most likely running lean & causing the detonation. Cold air induction would probably help. A friend cured his detonation problem by fitting an engine cooler. Pistons ran cooler & those few degrees made the difference.