Complex sentence: The locomotive had a Belpaire firebox and, instead of the usual deep bridle casting, was built with a shallow casting and frame under the firebox, which permitted all firebox stays to be removed without lifting the boiler from the frame.
Split into simpler sentences: The locomotive had a Belpaire firebox and, instead of the usual deep bridle casting, was built with a shallow casting and frame under the firebox. This permitted all firebox stays to be removed without lifting the boiler from the frame.