My rear brakes hang up when I park my 72 z. When I drive it there seems to be aslight drag at low speeds. Any ideas (I've adjusted the shoes with no success) Do I need to replace wheel cylinders ?

Try checking the backing plate that the shoes slide back and forth on. It may be dirty, rusty, or maybe just not lubed where the shoes contact it and slide. If lube doesn't solve the problem, take the shoes out, use a wire brush to clean those contact areas and get them smoother, and paint w/ epoxy paint. After its all cured, lube those points and reinstall the hardware and shoes :-)

I sincerely doubt that dirt or the backing plate being rusty is the problem. The return spring will overcome any dirt. I think what you said is the cause. The wheel cylinders are either stuck because of rust or they are frozen in place. If you can take them apart and the cylinder is not pitted , they can be rebuilt. Kits are available. If pitted , replace them. If the piston in the cylinder is stuck or frozen in place it cannot allow the shoes to return to the relaxed position and they will be against the drum. Gary