I'm running an aftermarket pedal setup that uses an OEM throttle cable for a 72 Camaro w/a 350 (21"). The pedal was installed by a previous owner so I'm unsure from whence it came or who made it but it works pretty good. I fit the cable after some trial and error. A 19" or 20" would fit better btw.
The pic isn't that good but should give you an idea. I can provide a better pic if needed.
Pic
