Several of the CSAR's Class 6-L1 to 6-L3 locomotives were modified by P.A Hyde, Chief Mechanical Engineer (CME) of the CSAR, by having their round-topped fireboxes replaced with larger boilers and Belpaire fireboxes and by having larger, more sheltered cabs installed.
During the 1930s, many of them were modified once again, when the CME of the SAR at the time, A.G. Watson, reboilered them with round-topped fireboxes once again, but retaining the larger cabs.