Nick, I have never quite understood the CRMC, 'they' want to reproduce 'of the period' racing, but allow not 'of the period' engines and modifications - like the oversize triples you detail.
I remember in the 80s having a conversation with 'an official' and when asked about thoughts I said overwhelmingly officious and overbearing, he was surprised at my statements! - only changed later when Ian Johnson (spelling!) became involved, more relaxed and friendly with common sense, better grids. Apparently has now gone back to the way it was - pot hunters throwing money at machinery.
PEH, Cadwell is fun because it is so narrow - it demands 'focus'. I remember Dave Hallam on his TZ750 outfit failing to turn right at park corner, the front hub ended up buried in the gearbox.
Oulton Park events are now limited due to newcomers and noise limits. The government refuses to grant 'grandfather rights' to circuits every time they are asked.
Chris Vincent's TT outfit was initially an A7 based engine, he later moved on to BMW engines to go faster. For mainland Open class events he used an A65 engine.