May I suggest that you define the end uses of the car BEFORE making any decisions on parts? Determining if the "body roll" is excessive or normal is something that an experienced B body owner would be able to define for you after a short ride. I don't think there is much other way.

What, in your opinion, makes "Hemi" springs "better"? Again, what are your goals? Heavier springs (and torsion bars) could show an improvement for some goals, but not for others. Bigger (or stiffer) is not necessarily better. Which is why ALL B bodies didn't get the same springs or torsion bars.

In 1969, heavier springs were added to control the rear suspension when applying power. And in doing so, ride was sacrificed and, to some extent, handling. A perfect example where bigger (heavier) is good for some things, but worse for others.

Define your goals and ask here for suggestions on how to achieve those goals. Asking 'should I do this or should I do that' will usually be answered with 'that would depend on the intended usage'. But the massive amount of experience here can help keep you on the straight and narrow.