Complex sentence: Later some of the GEC Alsthom units received an internal overhaul and a first-class section was added; these were numbered 465201-465234 and are now numbered 465901-465934 and are known as Weald units.
Split into simpler sentences: Later some of the GEC Alsthom units received an internal overhaul and a first-class section was added. They were numbered 465201-465234 and are now numbered 465901-465934 and are known as Weald units.