Yes, you can create a custom JB 4.3.2 ipsw to maintain the unlockable baseband and update to the latest firmware.
It will be untethered even if its new or old bootrom 3GS iphone.
Thanks, that I know it's just that my old 3GS was the old bootrom so I did not have to worry and did not stay up-to-date on the bootrom news about the newer one.
I just picked up the phone updated to 4.3.2, unlocked it and all set to go.