NOT an "S-Code", but should be close to the same, my 11/2/66 San Jose engine bay was painted as such:
* Cowl Area ~Fading to the red oxide sealer/primer (salmon-colored) a few inched below the transition to the trans tunnel and no black or very little black by the time you get to the crossmember for the transmission.
* Torque Box, drivers side ~Down to the leading edge corner of the torque box and over onto the side of the frame rail (rail going under the floor pan) about even to where the angled portion of the floor pan meets up with the floor pan that is typically horizontal of a car sitting on its wheels. This black oversprays a little rearwards at that area (as Bob mentioned, no distinct line)
* Right side (mine is coupe, no torque box) ~Sprayed rearwards towards where the angled floorpan reaches the horizontal floorpan, a transition very close to this point (some red seen along the angled floor so the black did not go all the way down
* Bottom side of frame rails and cross braces ~Red Oxide primer/sealer (salmon colored)
This above is going by memory, I have pictures I can provide but I'm not sure I can easily find them. The pictures are posted in another thread of my example. If I can locate them easily enough, I will link to the thread. It might be a while, later today before I can search...I have other plans for the day at this point in time.