Shan-e-Bhopal - तेरी खूबसूरती से नजर नही हटती, नजारे हम क्या देखें - ललितपुरी रेलफैन

The MG portion of the North Bengal express ran as an express between Manihari ghat and Siliguri and thereafter as a slow train till Amingaon with many stops.
In 1964, the Farakka extension was constructed and the North Bengal express was diverted to terminate at Farakka. At the same time, the Old Malda- Chamagram line was constructed on the other bank. On 1st April 1964, the broad gauge line from Khejuria ghat to New Jalpaiguri was opened and the old MG North Bengal Link express was diverted to start from Khejuria ghat (near Malda) instead of Manihari ghat. This new BG avatar was renamed as the Darjeeling mail.
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meter gauge Assam link express continued to operate from Manihari ghat.
Note that in 1964, the BG line terminated at NJP. The NJP-Fakiragram-Amingaon section was still MG. So, the new BG Darjeeling mail terminated at NJP. This soon became a very popular train. So, when the BG line between NJP and New Bongaigaon was opened in 1965, the Darjeeling mail was not extended.
As far as trains to Guwahati were concerned, it still had the Assam mail (with a connection to Delhi) and later the Kamrup express.