When the clock was converted to electric drive the back arbour supports were cut down. As the fly was no longer required (in fact it needed to be removed to connect the motors) these post could be cut down to make room for the motor to be mounted.
This seems like a terrible way to do the conversion. The Church Buildings Council of the Church of England provides guidelines on maintaining turret clocks which states, with regard to auto-winders and electric drives, “No parts should be removed from the movement.” and “There should be no cutting or drilling of the clock frame.” It’s likely that this conversion was done a long time ago, long before these rules were written, and was probably just how things were done then.
As they are cast parts welding a piece on top wasn’t going to be easy. Instead the top has been milled perfectly flat and an extra chunk has then been bolted to the top. The sides of the new piece were then milled to match the existing sides. The holes were plugged by hammering in a core of the same steel and the top shaped by hand to match the existing pillars. A hole was then bored to take a new bush (not yet made).