Hello from Lo-Fi! I have made this conversion kit to rescue your Fuji FP-1 from the shelf or attic. The loss of Fuji Fp-100 and other options of packfilm was a crushing blow for many of us who had this camera. I want to help you bring your camera back to life with this kit. 
This kit replaces the packfilm back on your FP-1 with a custom designed, easy to install Lo-Fi 4x5gl back(gl is graflok). This means you should be able to use any graflok based film carriers with it. The kit includes two lens stops, one for the standard film plane, and one for the Lomograflok Instax Wide back! 
The kit can be installed by removing the 8 screws that hold the packfilm back on, and putting this back on with the same 8 screws! The conversion will likely take 10-15 minutes on average. 
The kit comes with everything needed for you convert your camera to use 4x5 graflok backs. The kit does not include: actual graflok backs, the Lomograflok, or an FP-1 camera.
Keep an eye out for my other new products, my lofianddiy blog, and my youtube channel of the same name! Thanks for your patronage!!