I downloaded the India, Singapore, etc. v20H Stock ROM with great difficulty from the link in the OP.
I am sharing the Stock ROM and is shared here for anyone who needs it.
Files available in the share:
There's a new update from LG for India. I am now on v20i and the baseband is 1035.21_20120327.
Android version: 2.3.4
Updated using LG PC-Suite.
Just trying to help as I too had issues and this is the mistake I was doing...
Wondering if you are restarting your phone at least once after changing the IMEI... i. e. booting back to the Stock ROM. It may not work if you restart/b...