Thanks Bryon,
I should have visited the *Options* page in the CRG archives first..
The following statement from the first link makes it seem both were available for the complete '67/68 years..?
"In the first two years, a cowl plenum air cleaner and/or headers were available as part of RPO Z28."
PS. ... saying 'as part of' makes it seem they were included with Z28 option; whereas weren't they really available (with Z28) as separate options?
Better wording?? "For the '67 and '68 model years, options for 1) cowl plenum air cleaner and 2) headers were available separately or in combination, only if RPO Z28 was also included."
... and yes, they were expensive... but a bit less so if you ordered both..
in fact, if one of those options were desired, I'd guess most ordered both as adding cowl induction only added $65 to the headers only list price?