We recently acquired a 1982 Honda Civic Wagon with only 95,000 miles. It's in great shape, but started making a knocking sound from the rear. The brakes are also a little jumpy, but all is well if I down-shift to brake. The car isn't shimmy-ing, but the knocking is problematic.

Could be several things. Bearings in the rear can make noises like you describe and so can a loose exhaust system. Best to have it checked out if your not comfortable doing the repairs. The brakes being touchy could be from the car having sat a lot. For its age that's low miles so most likely wasn't driven a lot and could be some rust on the brakes.