Rear end control

A friend who developed a disease and can no longer drive had bought new in 2007 a gt500 of which he promptly sent to Sean Hyland to convert to Super Snake status.

Fast forward 9 years later in 2017 and after only 18,000 kms put on the car, my cousin purchased the car and he really enjoys it but is terrified at loosing the rear end of this car, he along with the car resides in Montreal.

Can someone make a recommendation of what is needed to better control the rear end, what bolt ons, where to start.

Skip all the lesser offerings and jump right to Maximum HD lower control arms + relocation brackets, Panhard bar plus a set of Bilstein shocks all round.

Thanks ZR, have forwarded the info. By HD you mean heavy duty right?

Yes sir.
Above is assuming he's already done a decent set of tires.