Ok, it's an hard work but we have to start in order to obtain some progress, so here's the place where to discuss/share our consideration on the PKG file structure.
I attached a picture of the pkg header of Flow USA, so we can refer to some real offsets when discussing about it.
I signed the first, easy and noticeable structure:
1) Blue (offsets 1C - 1F): Global pkg file length:
-- It's sure, total file lenght = 131.017.248 bytes so 7CF2A20
2) Green (offset 2C - 2F and F0 - F3): contained file length.
-- It's a supposition, contained file lenght should be the pkg file lenght - the pkg header lenght, so could be 131.016.832 bytes so 7CF2880
3) Red (offsets 30 - 5F): Code name of the Demo/Game:
-- It's sure, there are 12 double words reserved.
Please, share your findings here so together we could find something useful to understand those interesting files