I've got twin throttle cables on my car which connects to a twin spring Magard thingamyjig. I may have got entirely used to the feel of the throttle in my car but I have driven a lot of TR7s and TR8s in recent years and I have to say that I haven't noticed any difference even when the cars have been left hand drive and the throttle pedal is right up against the gearbox turret.
I think we need to get your car alongside some other TR7s we know are 100% right and check to see if there really is a difference.