Or, another way to put it, a Z-bar lifts the outside wheel. In effect, it reduces roll stiffness, without changing basic spring rate; while a sway bar increases roll stiffness.
Certainly would do nothing to solve the problem I was trying to solve; which is that the TR3 rear suspension lacks enough rebound travel. With the factory setup, in a hard turn, the inside wheel runs out of travel and hits the frame. The sudden impact is what upsets the car's handling so badly ... if you are lucky, the rear end just 'steps' sideways as the outside tire loses traction (due to the full cornering force being suddenly transferred to it), which unloads the inside spring and allows the inside tire to sit back down. It's a rather amusing effect actually, if you are expecting it.
Since the Z-bar reduces roll stiffness in the rear, it also increases understeer (which IMO a TR already has plenty of, especially if you are running a front sway bar or have increased the front spring rate).