The files uploaded by Mickey Mouse here are the ones which finally worked well for me.
They have converted my V804SS to a full fledged Z540 - everything seems to be working fine.
You should note that with the Chinese version the modem responds to the AT commands:
ATQ0V1E0 - OK
AT+GMM - SGH-V804
ATI1 - Manufacturer: SAMSUNG ELECTRONICS CORPORATION
Model: SGH-V804
Revision: V804GSMCN
IMEI: 35832***********
+GCAP: +CGSM,+DS,+ES
The modem seems to have the V804 string, but after upgrading with the Singapore version supplied above the modem now responds as follows:
ATQ0V1E0 - OK
AT+GMM - SGH-Z540
ATI1 - Manufacturer: SAMSUNG ELECTRONICS CORPORATION
Model: SGH-Z540
Revision: Z540DZFE1
IMEI: 35832**********
+GCAP: +CGSM,+DS,+ES
The string is now SGH-Z540 & now the phone is syncing back to the PC.