I used a Lokar "through the floor" throttle kit on two of my projects already.
These use a simple "bell crank" styled cable hook up. You just drill a a small hole in the floor to accommodate the bell crank end and screw the pedal assembly down to the floor. Then it's just a straightforward cable connection and throttle return spring at the carb.
You'll get a lot of firewall real estate freed up under there without all that linkage stuff hanging around.