if its going to be a built for high power tranny, i'd go with the c-4, its lighter weight, so it'll put less of a load on the engine, and also keep the vehicle weight down as well.... the other option i'd reccomend is an FMX its somewhat the predecessor of the c-6, but as far as i've know from experience, are a lot tougher than the c-6 and weigh in a little lighter, the only thing with them i've been annoyed by, is when running them on a 302, you've gotta get the 351 flexplate to fit for the starter, i messed with that problem for a long time, and transmission shops had no clue what i needed