Question about headers

I usually go with the filesize (in the case of FF3us, 3073KB for regular headered ROM or 4097KB for expanded headered ROM) or just open the ROM and look at the first 0x200 bytes. If they are mostly 00 the ROM has a header. I usually also use the hex editor to remove or add a header (in the case of adding one I just add 0x200 time 00 at the beginning).