What are you calling a "sub rail"?Is Bob Drake the only source for 39 coupe sub rails.
I have restored lots of efv8's and have replaced or repaired floor pans rocker panels, etc and have never heard anything on these cars called a "sub rail". This sounds like model "A" talk.It referes to the outer edge of the floorpan. It runs from undeneath the cowl all the way back to where the frame kicks up over the axle,it sits on the frame then the floorpan on top of it. I see them also refered to as rockers.