so do you mean the frame rail that runs under the floor up to the inner wing or from the floor edge forward towards the front.either way there should be little difference between left and right hand cars apart from your mount for the clutch cable and some of the holes for fixing the brake pipe mounts and the fuel lines which would not be a problem. i have got a LHD 240Z and RHD fairlady (260) so i can compare.
your blue/red stripe and blue/white stripe is for a power antenna and the other white and white/black only shows up on later wiring diagrams as speaker connections.i hope this will help.
i have got a US spec 1971 240Z and where the power aerial and marker light is i have also got two spare electrical conections.i thought they might be for a rear fog light to connect to but i have been unable to follow it by the wiring diagram.