What's your stock set up and what intake do you have now. Say if you started with a 318 2 barrel and added a aluminum 4 barrel intake you will need a 340 throttle cable bracket to get full throttle opening.
I think you may be on to something here. Yeah, the car started life as a 273 2bbl. I got a 4 bbl throttle cable, but I think the throttle bracket is the original 273 unit.