Sorry about the late reply, I got a similar brick because my partitions were incorrect when I was restoring a nandroid backup.
Check if you can get into fastboot, and use Mur4ik's bootloader builder to set 150MB system partition for GB, then try to flash again (this is only if you have access to fastboot.)
If you can only get to download mode, your only option is to flash 2.1 with fastboot through KDZ, then flash GB again however if you have resized partitions it could cause more problems because I am not sure on the 2.1 size (it is LG's 2.1 afterall)
the KDZ could have a MBN file in (used to resize partitions) and it could flash a new bootloader with the right sizes but I am not certain (never decompiled a KDZ myself)