Do I need bigger torsion bars?

The ride height is irrelevant because you set that with the torsion bar adjustment screws.

The slant 6 cars used a lower spring rate torsion bar than the v-8 cars. The slant 6 bars will allow more body roll, but are desired for quarter mile racing because of the weight transfer is better for racing. If you are not going to race it, then you may want to consider changing the bars.

You then have to ask, "how important is handling to me?"

If you want it to handle better, then you may want to consider upgrading the torsion bars when you have the time and money. They had different torsion bars for the different v-8 engines and performance packages through the years. Those will handle better than the stock slant 6 torsion bars. However, since torsion bars are basically springs, they do fatigue and will eventually get weaker and sag and eventually break. I would recommend if you are going to replace them, to buy new ones and consider upgrading to 1.00" or 1.030" bars for better handling.

If you want to really handle better, add front and rear torsion bars.

It is how much you want to do...