It took me about a year of noodling around, but I have finally arrived at a solution that brings my instant photography game into the modern age. And is pleasant to work with. The truth is, I haven't been particularly happy with the current version of Polaroid instant film exposed using my vintage SX-70. On the other hand, while it seems that Fuji's Instax film is the best current option, their cameras are, shall we say, pretty bare bones affairs.
The monstrosity pictured above is the solution I've come up with, and is comprised of a 100 mm f/3.5 Mamiya Press lens, a Cameradactyl 3D printed body, and a Lomograflok film back. The benefits of this system on paper are the quality of the lens and the exposure control it offers. We'll see how it works in practice over the holiday weekend...