Just found how to install the illusive iff plugin for Gimp that works in Linux. To get iff support in Gimp linux, specifically Ubuntu /Debian. After installing GIMP run:
sudo apt install libgimp2.0-dev
git clone
https://github.com/unwind/gimpilbm
cd gimpilbm
make
make install
In case you get an error you're probably missing build essentials, install
sudo apt-get install build-essential
and repeat steps above