I have been wanting this engine for some time....so what number 304 or 320. After looking up the information in all my reference books it was rarely photographed. But the facts are it was delivered in 1950 numbered 320 just as Lionel shows in there art work. Around mid 1952 the number changed to 304 and it remained 304 until retirement in about 1965. The 304 looked like Lionel's art work up until late 1956 when the "ST. L. S-W." on the sides of the engine were replaced with "Cotton Belt". In 1957 it received a one of a kind black widow paint scheme.
So in a nut shell:
#320 mid 1950 to mid 1952
#304 mid 1952 to late 1956 or early 1957.
I guess I will decide in 2 or 3 weeks ....... leaning 304