You could drop in a V8 but you would be spending a shit load of money. First you would have to get the motor, transmission (change the transmission tunnel if needed not likely though), rework your engine mounts, headers to fit the 5.0 and have enough clearance to work, possibly a new drive shaft due to the distance b/t the transmission and the rear axle, new exhaust system to run duals, and probably some other stuff.