Thank you for your responses !
The thing is the aircraft came with a single filament lamp (which was a 4591), but to get it to meet the DGCA requirement for night flying it needs to have two separate lamps or a single lamp with dual filaments. Now the installation of two lamps would require a structural modification to the cowling which I am not too keen on therefore I am looking for a simpler way out by installing a single lamp the dual filaments.
Surely this wouldn't be that uncommon a task..?