No harm in just flashing the modem without the RIL.
Seems that you're not the only one on Vodafone, India, with modem problems...
Galaxy S2 unable to register to network, no signal
As far as I can tell, there is no Vodafone specific firmware for the Indian SGSII. The JB firmware you are using is European based with a European, XX, modem.
The latest stock firmware for India is XWLPW
on Android 4.0.4. It might be worth installing that after a nandroid backup, to see if your signal improves as I'm guessing it has a DD modem. Alternatively you could just try flashing the 2 DD modems, here
Not knowing your exact location, here is the Vodafone India Network Coverage Guide
to check what they, "say", it should be.