iPhone Help with iOS 6.1.3 downgrade.

Hi, I have my friends iPhone 3GS here and he has asked me to fix it for him. When he bought it, he tells me it was already jailbroken and unlocked via the baseband on iOS 4.1, and he has accidentally allowed iTunes to restore it to 6.1.3. Now I have the phone, and I have extracted the blobs for 4.1 and 6.1.3, and I have downgraded the baseband from the 6.15 that it was on down to 05.13.04-6.4_M3S2 using redsnow 0.9.15b3. Now, with the blobs that I have and having downgraded the baseband, is it now possible to downgrade to say 6.1.2 or earlier in order to unlock it once again? At the moment it is currently stuck at the activation screen on iOS 6.1.3 with the downgraded baseband, and we don't know what network it was on originally so I can't put an original sim in to activate it.
Any help would be greatly appreciated,
Thanks
Bill

Never mind,
Just for future reference for anyone, I have fixed it as it had the old bootloader, so I didn't need blobs at all.
I just used sn0wbreeze to create a hacktivated IPSW for 6.1.2 and installed it with iTunes. All went well and I installed ultrasn0w from cydia (repo666.ultrasn0w.com) to unlock.