The first six locomotives were initially fitted with plywood sheeting over the cab-side windows as a wartime material-saving measure, with No. 21C107 "Wadebridge" the first to receive glass windows. Two of the front route indicator irons (of which there are five) were originally located on the smoke deflectors, which meant that the indicator discs stood proud of the casing. This necessitated a trial relocation to the smokebox door at the three and nine o'clock positions on No. 21C109 "Lyme Regis", and fitted as standard from No. 21C118 "Axminster" onwards. The batch constructed between June and October 1946 received a modified steam regulator and LMS-style parallel buffer casings.