Oh wow, I've been wanting to do this exact project for the longest time. Are you able to share anything more on the custom manufactured bits and pieces, how you interfaced with the chemical roller mechanism, etc?
If this works like the Polaroid SX-70 system, the rollers are just metal rollers a specific distance apart. They squeeze a package of chemicals inside the sealed film package and spread them uniformly over the film.
The chemistry of those systems is incredibly complex, but the mechanism is simple.
Me and a friend of mine made a prototype for one, using the internals of an impossible project phone ‘printer’. It takes standard 600 film. I had no idea that it would be the kind of thing hacker news would be interested in though.
Search the youtube and you will find a bunch of hacks people have done to use Instax film in MF and 4x5 cameras. I recall hearing some time ago of an attempt to make a Graflex back for Instax as a commercial product, not sure if that actually happened.
The chemistry of those systems is incredibly complex, but the mechanism is simple.