The 5-spd trans will probably need a clutch upgrade to reach the 300 ft-lb/300 bhp mark. After that, it's how many trips down the strip you make with high grip tires.
One other thing for macster. The torque converter isn't locked up at WOT, ever. So the torque multiplication happens a lot of the time when you stand on it. In fact, it is probably biasing your dyno readings (power down and torque up).
Peak multiplication is when a car is brake torqued and engine is at stall speed. Once above stall speed, multiplication drops to essentially 1:1. This link may help explain
http://www.bankspower.com/Tech_under...rqueconver.cfm
I also liked this video
http://auto.howstuffworks.com/mpeg/torque.mpg