Not sure if it's the same pedestal type, but on our '77 Hunter, the Edson pedestal has a bolt on the aft side of the pedestal as you describe, which anchors a small W-shaped clamp inside, which holds both throttle and transmission cables in place. Once you loosen it, you can wriggle the transmission cable out and pull it through (assuming you've already disconnected either end).
Getting all this to happen is %100 not fun at all and is way more difficult than it sounds (and I think it probably sounds difficult as it is), unless your arms are only about 1 inch in diameter. You'll want to disassemble as much of the binnacle as you can first, and invest in some of the longest needle-nose pliers you can find.