I had a quick look into some files from
here and they are all different from the DS1000Z. I looked into DS2000, DS4000, DS405X and DSA800 (which even doesn't contain a .GEL file).
DS2000 and DS4000 seem to have the same file structure...
*edit* Some more cleanups and the bytes 32-36 are 0x00070000 for every firmware, except for the boot update, where it is 0x000f0000. So I changed the default folder to $Device-$Version-$UpdateType...
*edit2* Probably last coffe break before the weekend; If you have PIL (or Pillow) installed, it will create a png like smithnerd did from the last file. Also did a few more sanity & crc checks, SparrowBootloader.sb should be written correctly now...
Also it always automaticall sets the output directory to $Device-$Firmware-$Type and now allows for multiple GEL Files. So "./unpack.py *.GEL" works properly now.