The whole point is to get rid of the bind created by the UCA's in an pre-S197 Stang. To do this, you need to remove them altogether. If one was to install only a PHB or WL and LEAVE the UCA's, what have you accomplished... nothing! You have just added time/expense/weight to you ride. You will STILL bind on axle articulation and will likely just add additional binding issues. The PHB will cause some lateral axle deflection and fight the UCA's or the Watts-Link will not be allowed to move freely as the UCA's will fight it as well. You need BOTH the PHB or WL AND torque-arm to be free of the UCA's.
I am in 100% agreement about sub-frame connectors. Get them welded in place and have uppers installed if you can afford to do so.
Not true my friend. The reason for the binding is the side to side movement of the upper control arms. Once they reach their limit, the tires lose traction and the suspension snaps back to center, which leads to unpredictable handling. By installing the panhard bar, you eliminate the side to side movement, leaving the LCA's and UCA's to 2 only 2 jobs instead of 3. Axle wind up and up down movement. The panhard bar stops all side to side loading on the UCA's so they can not bind anymore. With the panhard bar, you will be limiting the up and down movement untill you get rid of the UCA's. But you can't do that until you have the torque arm. Trust me on this, the panhard eliminates the side to side bind. I run this set up now, panhard and LCA's and UCA's and there is NO side to side bind like before. Its a half way step, but it does work, and its a hell of a lot cheaper than going straight for the torque arm.