G285 or G305 are internal drive identifiers - also used for doing a region code reset or when flashing a drive. Internally I also use these in Binflash to distinguish between drives. The "07" at the end of the file reflects the bootcode version - bootcode and firmware must match.
Getting the real drive from the ID is quite easy with Optiarc drives. If it starts with a Q use a 5, if it starts with a G use 7 as the first digit (*). Then take the next two digits (e.g. 28). Last digit modulo 5 for the 4th digit. If the last digit is less than 5 add "A" else add "S". Letters 'A' to 'D' correspond to '0H' to '3H' (on slimline drives)
G285 means 7280S:
G305 would actually mean 7300S but they still named it 7280S for whatever reason. Unfortunately Optiarc mostly seem to have stopped firmware support for their drives, so the only firmwares available were dumped from existing drives.
The G285 signature at the beginning of the firmware could potentially be used to prevent flashing from G305 firmwares to drives with G285 bootcode, although they usually take the first Byte of the firmware for this verification
(*) this is a little simplified
K->NEC ND (with a different usage of the remaining digits)
M->NEC HR (only known from the HR-1100A)
L->used for some NEC and early Optiarc slimline drives
D->used for duplicator drives (NEC and Optiarc)