This tulwar truly is an anomaly, and I have never seen one with one of these blades either. I agree with Rsword that the blade resembles those of Assam dao. With this region being far from the normal tulwar 'habitat', the first question is has been agreed, how long have these incongruous components been together.
From what I can see of the metal discoloration in both hilt and blade, both seem concurrent and it does seem the piece does have some age. With these things all considered, it would be difficult to identify the region of provenance likely for this weapon with any certainty. It is difficult enough to specify regions for tulwars, even without this blade anomaly, aside from the general regions associated with them, primarily NorthWest India.
If this sword is genuinely mounted in period, as it appears, it seems it quite possibly have been mounted for an individual in northwest regions with what have been a heirloom form blade. During the British Raj, there were many paramilitary and auxiliary units as well as police units. It is my understanding that these units often supplied personal weapons, and I wonder if either someone from Assam may have been in such a unit in the northwest, or if possibly there were such units outside the military in Bengal. Bengal is of course adjacent to Assam, and there were of course the famed 'Bengal Lancer' units, who did carry tulwars.
There are I believe dhas with blades like these as well (as already indicated) and given British presence in Burma and environs, the same thoughts may apply here also.
Pure speculation of course, but thought I would just add it just in case anyone else might consider plausible.
The 'smoking tulwar' would be of course if other examples were found with these blades, and provenanced!
All best regards,
Jim