Assamese and Bengali as Separate Scripts

There are only two differences in the transliteration table:

. . . . The Bengali alphabet repeats ba where va is expected.

Treatment in various sources

The ALA-LC Romanization Tables list Assamese and Bengali separately. The Tables are arranged by languages, but this enables the difference between the two scripts to appear naturally.
Unicode / ISO-IEC 10646-1 does not have a separate section for Assamese, but includes the two Assamese forms as additional characters under Bengali, with a note against each. This is because Unicode is dealing with character repertoires.
Maheshwar Neog writes on 'The Assamese-Bengali Script', where the singular noun refers to the historical totality in all its variety, but when the author describes the current differences he has to speak of 'the Assamese and Bengali scripts' in the plural (p. 22).

Conclusion

A transliteration table including the two scripts requires different forms of ra, and different entries under va. For the purpose of transliteration, the scripts are necessarily different.