I had the exact same problem. My gas pedal was low, bottomed out on the carpet before opening the four barrel, and I had the same 1" or so of cable slack that you pictured. I thought, "I'll buy one of the reproduction throttle cables because mine must be stretched." Turns out the repro cable didn't fix the problem, and, didn't work as smoothly as the original. Then I thought, "Well, maybe my gas pedal rod is bent" and bought another original gas pedal linkage assembly. That wasn't it either. Both my existing and the replacement has the same profile. I thought, maybe the cable retainer that attaches to the carburetor mount bolts is incorrect. Nope, that wasn't it.
Whether it is the correct solution or not I ended up bending the gas pedal linkage. Problem solved until someone can tell me where the discrepancy lies, but I feel I exhausted my options.
Brian H.