Try the battery, if you haven't already relocated it yet. Put it dead center or offset to passenger side to counteract your weight a little. Make sure it is well vented to the outside of the car, perhaps wheelwells?
Speakers? Lots of soundproofing close to rear wheels? I used Quiet Coat on mine, you could slather that on the floors to minimize road noise from the rear tires/suspension. Look into a solid divider between gas tank area and passenger compartment, there are a few made there. Kind of a rear firewall idea.
In general, I would prefer to add as much useful weight to the center and rear of the car (at or forward of the rear axle, of course) as I could, to help in both straight line and cornering traction and offset the weight imbalance of a RWD front engined V8.