I noticed this before my rod snap issue: The throttle seems to stop firmly with 3 or 4 notches left to go. I do note however that if I walk over to the carb the throttle arm on it is pretty much fully open. It maybe has 1/8" or 1/16" left that could be opened. Any reason the throttle lever is reading that it can go farther?
Carb throttle levers are different lengths on various years of carbs. Or the throttle lever could be bent wrong.
Carb pull rod may be too short or bent wrong.
Throttle rod lever on the throttle rod maybe wrong year, or could be bent to wrong shape.
Most times with worn parts on the Ford, the throttle lever can be pulled down past the quadrant notches.
What counts is the carb throttle lever should fully open and be stopped by the post stop on the carb, that assures you have the butterfly fully open for max speed. And when you close the hand throttle, the butterfly closes to the idle setting you set with the screw on the carb lever.
Where your hand throttle ends up on the quadrant depends on those settings. Strive to have a bit of carb lever open for setting idle, otherwise when you fully close the hand lever at the top of the quadrant, you could stall out the engine.
Turn the rod around end for end
If you haven't fixed your broken throttle lever rod, maybe you could set your carburetor throttle where you want it in relation to lever position at the quadrant and then weld it back together there. You didn't mention if it is a stock carburetor. I put a Stromberg LF on mine and it wouldn't idle all the way down even if you pushed the throttle lever up over the quadrant. Then I found out there is a screw that lets you adjust the arm on the throttle shaft.