What are these four pin components labeled LB-4 on a motor control circuit from 1979?
I agree, they look like bridge rectifiers (+1). They probably go to individual transformer windings (the center pairs of connections). You can check the inputs and outputs. They are unlikely to be bad, but it's possible. At least two rails appear to be zener shunt-regulated with the power dropping resistors (discolored PCB under them) and top-hat diodes. 

Design looks older than 1979 but with some newer parts. Weird hand-made Japanese-looking sort of, but no plated-through holes and no gold plating on the connector pins, very cruddy. If I were to guess I'd say ca. 1970 Taiwanese design. 

If the electrolytic capacitors are that old, they're all suspect, particularly the two larger ones. Check the ESR or just replace them. 

The green "bricks" are film capacitors.