There was only one line, the only place to shift the order once a body started down the Fisher side was at GMs scheduling bank. Fisher scheduled builds and balanced theload on their side based on their needs in building the body tub, like no convertibles closer than 12 to 15 bodies, no Vinyl tops closer than 8 to 10 bodies, etc. GM had different scheduling issues, like A/C, R/S, console cars, but could care less about a convertible, or vinyl top equipped car so they needed the scheduling bank to shuffle the cars around to suit their needs.