I guess all I needed was to look it up in the 1967 Camaro AIM. This clip from section M20 Sheet A6 clearly shows that the speedo cable mounting holes would be drilled only if the car came with a Muncie 4-spd and an L48, L35 or L78 (aka 350 or 396). My car clearly has these holes which appears to be factory drilled so yay for me...
Chris