Dan. I'm not a purist nor knowledgeable of how Ford routed the cable for Concours judging of your car . . .
I would go straight back from the control handle through the firewall with the cable (keep it straight), then make a smooth curve down and toward the driver's side of the transmission. I'd stay away from exhaust headers and exhaust header pipes. My recollection is of a single clip type bracket that Ford used originally. The clip was secured by one of the transmission side cover bolts to guide and stabilize the cable connection to the mechanical arm on the R-10 overdrive unit. Probably the single cable retainer clip was located on the top rear bolt of the side cover to reduce the distance from the retainer clip to the overdrive mechanical engagement arm.
I'm rusty on this, but am guided by what you're trying to mechanically actuate. Heat from the exhaust manifold or the exhaust header pipe will accelerate corrosion of the cable outer jacket and destroy any lubricant used between the wire control wire and the cable jacket unless you're using graphite only
Hope this helps. I'm sure others will have additional information.
Hey. You're getting there!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York