yes the torque is an issue of the big cube pontiacs but for a stock'ish 455 or even a well built 400 street motor a goood 200r like from a GN or SS monte etc will usually be ok if not beaten & abused, thats what they were doing back in the 90's before shops like EA & art carr were beefing them up like today. performance pontiac had quite a few articles on doing the 200r swap & said you wanted a good one from a GN etc & in stock form they did great for the most part.
obviously today they should be build to handle the power of the engine & set up right, or just go 4l80. for now im content with my th400 & lower number gears, 3.23 are manageable for all but long interstate trips, which i dont plan on taking in this car. & i have another "slow" t/a with 3.08s if i felt the need to take a long trip on interstates with 70-80mph speed limits.