This is not a custom rom.
It's only rooted official GB stock (v20f)+1.5 OC kernel+some tweaks nandroid backup.(on su660)
You can use this if you have su660.
Restore only boot & system with CWM's advanced restore.
You need not to wipe.
(But you have to backup for undoing always. Some ppl can't boot with OC kernel caused by low level board.)
Then you will have rooted GB 2.3.4 stock+1.5 OC kernel rom with your data.
But time will be faster 9 hrs than it caused by different baseband.
You can set time manually at setting .
Official updater doesn't extract *.fls any more. And I can't give you baseband.
---------- Post added at 12:41 AM ---------- Previous post was at 12:12 AM ----------
To root v20f is not simple and has risk.
Because of it has locked bootloader.
It needs definite understanding of nvflash and smartflash for undoing.
I can't this explain.
If you have Korean friends, request him to explain this
He will have to register unless he has ID at Naver.