drill a big enough hole in the firewall to allow for the rod movement. run a straight 2/56 rod back to a servo with no bends, kinks etc. This may require moving some things around,. but it will provide a slop free smooth linkage that will never let you down. Nyrods expand and contract with heat and are poor choice for precise throttle control. Anything like bell cranks etc adds slop and is more complex then it needs to be. I set this up during my planing stages so the gas tank, servos etc are in the right place. A retrofit may not work without some compromises.