[spdbrake]

Check the nuts on the forward trailing arm mount. They point down and the frame has slots for toe-in-out adjustment. If the nuts are loose it will shift around on side loads.

Also check the outboard axle bolt (yours should have a bolt, early cars had a retaining nut) under the pin drive hub to see if it has backed out allowing your hub and brake to slide in-out. The caliper probably won't keep the wheel and hub from fully exiting the car if it comes fully undone.

The rear spring lower perch rubber pad disintegrate over time as well as the rubber bushings in all the suspension pivot points but that is a sloppy handling issue usually not a clunk.