P.S. for our younger readers, four bay bodywork means that visually, there were four side windows BETWEEN the bulkheads, i.e. between the rear of the driver's cab and the front of the boarding platform.

Five bay bodywork, therefore, means there were five shorter window pans between the bulkheads.

Look at a CIE RA class. They were very unusual in both Britain and Ireland in having seven bay bodywork. Although the last bay was slightly shorter.