Let's recap - you have a C4 and 8" rear and want 600 hp. One of two things is going to happen: (1) you will do nothing but spin the tires, or (2) you manage to start getting traction some kind of way in which case the 8" and/or C4 and/or driveshaft will break in short order. If an axle lets go you will make an immediate 90 degree turn.
You need to rethink your driveline before trying for that much power.