Midway through the manufacturing phase, it was realised that the locomotive would be considerably heavier than had been anticipated. In response, some elements were rapidly redesigned so that it could still confirm with the requirements laid out by the corresponding British Transport Commission specification. These late-stage design modifications included the replacement of heavy sections with lighter alternatives, such as an aluminium body and fibreglass roofing, while weighty electrical equipment was substituted with lighter counterparts wherever it was practical to do so.