Most guys, including myself, when adding an extension add around 5 ft lbs depending on length of the extension.
Ex: I torque Class 8 truck lug nuts to 550, adding about 10 ft lbs for the big ass extension I always use as well.
I can't speak for the transmission in the GT350, but adding an aftermarket cooler can be as easy as drilling and tapping the case and hosing up a cooler with an external pump assembly.
I'm a diesel tech by trade, so my trannys are considerably different. Most having ports already made into...