Simplify the following text for a Grade 6 native English-speaking person.
Original: The class , numbering 230 examples , was built by British Railways ' Swindon and Doncaster works in 1957-1962 and numbered D2000-D2199 and D2370-D2399 ( later 03004 to 03399 ) .
Simplified: There are 230 members of the class and it was built by British Railways ' Swindon and Doncaster works in 1957-1962 . They are numbered D2000-D2199 and D2370-D2399 ( later 03004 to 03399 ) .