Is it the sticker on the air cleaner????

I think it comes down to the intent of the factory, /6 was the baseline so every engine offered above base with more power is technically a performance engine, people upgraded to say a 318 over /6 cause it gave extra power, does that make it a high performance engine, no. But clearly 340, six pack engines and hemi's were obviously factory offerings as performance engines and sold as such. Engines like the 440 could be both depending on the car, wouldn't say a 440 in a land yacht is necessary a high performance engine but in a Dart, Cuda etc.. It is.