We have been running 904's several years, in both our cars, 3000 lb. Dart avg., 1.34 60' time transbrake, in a bracket race mode with lots of passes, with nothing more than clutch wear. Our Cuda broke an output shaft once in the middle of a wheelstand, but it was 3700 lbs and 1.40 60' times footbrake, but your dealing with 30 year old parts and your putting 2-3 times more torque to it than the chrysler engineers ever dreamed.