The CRG has a really good report on shifters, linkage and knobs. The correct knob is stated to be 2-piece black and chrome with shift pattern.
Here's the link:
http://www.camaros.org/shifters.shtml
The '67 AIM shows the 2-piece knob but doesn't specifically include the L78. It may be that the knob revision of 3-10-67 was prior to L78 production.
The '68 AIM show the 2-piece knob and states "12000 EXC. PROD V8 ENG & RPO L30-L48" in the title block. I believe this includes all big blocks.