I have a 69 conv and have looked at these areas, too. You do not need a rear sway bar. In fact, it can generate unwanted oversteer. However, subframe connectors can be a worthwhile benefit depending on your driving. I personally feel they are a worthwhile improvement for the added body rigidity. You should also ensure your body mount bushings are in top shape. I found mine to be rotted out as well as the subframe holes they mount in. This necessitated welding repair plates in, installing new bushings ( solid ones ). I already had welded connectors that I had to cut the welds to the floor and then reweld but that's a story in and of itself! I think anything that contributes to the structural stiffness is helpful. You can research this here doing a search as well as also visiting websites such as Global West's, Art Rasmussen's, etc. Good luck.