Tom,
So the 2.4S with it's forged pistons and forged and nitrided rods falls into the heavy duty engine category. Add to that an excellent oiling system, 8 main bearings (rigidity) and the natural balance of a flat six, where's the problem. My guess? The bottom end is likely good enough for 8500 without being touched. It's also very easy and very common to convert a 2.4 to a 2.7 as they share the same crankshaft. The 2.8RSR has the same stroke and likely the same crank, although perhaps race prepped.
The missing part of this equation is the valve train and port sizing. I don't think it's unrealistic for this motor to have ported stock heads and a hot cam. Also the 3.0 Carrera RS has only 8.5:1 compression and max power at 6200, not high enough to make power where needed to achieve 165, it does have a top speed of 152 listed though. At 226HP it doesn't make much more than a carbed 3.0SC suggesting small ports in the heads (the peak HP RPM also suggests this)
The 2.8RSR as I stated earlier made max power (308) at 8000rpm, the redline has to be higher than that to be practical as a track car otherwise you'd be shifting right at the peak with no headroom to wind out a gear a little further. The more I investigate this the more plausible it becomes. (and the more I want similar parts on my motor)
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1966 912 converted to 3.0 and IROC body SOLD unfortunately
1986 Ford F350 Crew Cab 7.3 IDI diesel, Banks Sidewinder turbo, ZF5 5spd, 4WD Dana 60 king pin front, DRW, pintle hook and receiver hitch, all steel flat bed with gooseneck hidden hitch. Awesome towing capacity!