The Colas 47 on offer from Bachmann is 47727, as far as I can tell.
It would be ok to use for renumbering as 47739, but you will need to change the buffers (to Class 60 type) and possibly add some pipework on bufferbeam area from looking at photos.
47749 has different cab ends to the other two, in that it has different type lights, so would not be an accurate renumbering.
If anyone can list any other differences, I would also be interested in hearing them, as I have pre-ordered two of the 47727 Colas models.