A PILOT EXPERIENCED A HUNG NOSE GEAR ON RETRACTION AFTER TAKEOFF. NORMAL AND MANUAL ATTEMPTS TO EXTEND THE NOSE GEAR FAILED. WHILE CYCLING THE GEAR, THE PILOT EXPERIENCED POWER LOSS TWICE ON THE LEFT ENGINE, AND THE RIGHT ENGINE HESITATED ONCE. ADJUSTMENT OF THE FUEL SELECTOR HANDLES RECOVERED THE ENGINES. THE PILOT CONTINUED TO FINAL APPROACH CONFIGURED FOR LANDING WITH DEFECTIVE GEAR, WITH FULL FLAPS AND MAIN GEAR DOWN. THE PILOT RECOUNTED HE HAD NO POWER RESPONSE FROM EITHER ENGINE BELOW 400 FEET ON FINAL. HE INCREASED HIS DESCENT ANGLE TO MAINTAIN 100 MPH BUT HAD INSUFFICIENT SPEED TO FLARE FOR TOUCHDOWN. EXAMINATION OF THE AIRPLANE SHOWED THE CAM ROLLER WHICH CENTERS THE NOSE WHEEL ON RETRACTION HAD FRACTURED, AND THE NOSE GEAR DRIVE TUBE BUCKLED AND FRACTURED WHERE FUEL SELECTOR HANDLES ATTACH TO CABLES TO SELECTOR VALVES.