You should be able to find a universal cable at any parts store, also at most farm stores, too (like TSC). I'm not sure how the knob come off on the '54s, I know that some have a set screw that goes in from the bottom. As far as removing the cable, don't cut it! There is a nut (should be 9/16" hex) on the backside under the dash. You will have to remove it from the carb and feed it back through the firewall, then take off the nut, and the cable should slide right out, housing and all.
