Are these torsion bars gonna be too big for me?

I think they'll be fine. It really depends on your own personal preference. I wouldn't run anything less then 1" on an A-body, but that's just me.

As far as what they came with from the factory, all Mopars from the era were drastically undersprung.

As far as the torsion bars improving cornering, they'll help A LOT. Body roll is largely dependent on the spring rates. True, a sway bar will help body roll without effecting your ride quality as much. But, its kinda like all the antacid commercials- a sway bar helps body roll after it starts. Larger torsion bars will prevent a lot of the body roll from ever happening in the first place.

A 1.03" bar should work out to be around 200 to 225 lb/in. A 1" bar should be between 190 and 200 lb/in, its really not a huge difference. And the rates do vary from manufacturer to manufacturer, that's why I listed ranges. I think I 1.03" is still a streetable bar, even in a /6 car.