i was in Bankura, west Bengal, 200 kms west of kolkata due to gearbox trouble. went to the local station, asking at the ticket desk what to do to put the bike on the train. they've suggested me to find the man who cares about mail wagon and its stuff. he told me to back, with the bike straight on the platform, the next day at 4.00 am, 2 hours before the train left to do all concerning. he booked me the place in advance then, once i was there at the right time, i had to disconnect the battery and get the fuel tank empty. then we put, we were 5 people, the bike on the mail wagon. it wasn't so steepy. i've "payed" the porters with the gasoline i had to left at the railway station...
ah.. i was traveling on the same train of course.
once in kolkata i had to manage the bike unloading by other porters: it wasn't so difficult, but i do not remember if i had to pay something to them, anyway it was cheap for sure. also do not exactly remember how i had to pay for the train transportation but it was something about 20 euro including my fare.
in kolkata you can get in touch with Eastern Bulls wich are a group of enthusiast enfield riders as you, i assume, will need some help on what to do or where to go in case you have to get , if possible, your bike fixed there. they were very helpful: came to pick me up at railway station and carry me to a budget hotel nearby the forwarders area to manage the bike shipping to BKK.
hope this helps you.