Buy a Miata, turbo stock motor or install LS3, and enjoy your Supra for what it is.
Seriously though, aside from the driver power seat, nothing in the interior makes enough of a difference to make putting up with a rattle can car worth it IMO. Replace the seat with a Bride or something of that type, start working out (skinny driver can make a difference), and relocate as much weigh to the center of the car as you can. Then if you're really serious about it, start replacing parts like your wheels, suspension, and brakes (all your unsprung stuff) with as light as you can afford. Still not good enough? Start swapping out body panels for carbon fiber.
Consider this: balance is more important than any one number.