The transducer is housed in a cube shaped frame. The transducer surround is made of stamped metal with four screw tabs, and the diaphragm is dome-shaped, and about an inch in diameter. A separate matching transformer is used. Note the black, gauze-like material covering the transducer: it looks just like a nylon stocking, or, given the date, may even be a piece of silk stocking material. Whatever it is, it still has some resilience which we didn't want to test for fear of tearing it.
Here's the transducer inside the suspension frame which is curved to conform to the die cast body of the 55C. Note the use of tension and compression elements. Oval rubber isolators (which became rather brittle over time) are placed over steel tabs that protrude from the U-shaped frame. The curved frame is attached with springs and kept at a distance with more rubber pieces.
The designers obviously thought a lot about the vibration sensitivity of this mic and wanted to make sure that the transducer was well isolated.
Here is the entire transducer assembly and transformer being inserted back into the shell of the 55C. This has to be one of the most elaborate dynamic microphones. Shure engineers were still in the refinement phases of dynamic microphones in general, it seems.