To call it an "option" accertains it could be ordered. An example you use of the Chevelle (and, I'll add, full size models), not having bright accents, implies that one could order the accents if desired. That was not the case. The engine packages either had or did not have these accents depending on the model car the engine was installed. Not all L48 (300hp) engines were created equal. That has been discussed on this site and I have owned and pulled enough of these engines, BITD, to know that only the Camaro/ Nova had "accents" that consisted of a chrome air cleaner lid and a chrome air cleaner lid ONLY regarding the 69 and 70 model years that I sought at the time. The full size L48s, and this is not a hard and fast rule, did not have 4 bolt mains either. Other than that, these engines, no matter what installed in, were the same.
To further clarify, I have never seen a 69 Chevy L48 engine with a factory chrome oil cap. I have never seen a chrome oil cap on anything other than a BB in a Camaro, Nova, Chevelle or Corvette and only on the sb Z28 Camaro and Corvette.