The Polaroid back that takes pack film (I prefer 665p/n, ymmv) fits really nicely on the back of an ICA Ideal 9x12 with a bit of careful work and gaffers tape.
Shoot about 3 stops bigger/slower than you would normally and the negative will be nice and rich. The positive on the other hand, well...it'll be lomographic.
Interesting thought; only a year ago I sold my Voigtlander Avus (in near mint condition) with matching 120 rollfilm back to a friend who immediately put it back into professional service; raised a few clients' eyebrows to say the least.
The main issue remains: the emulsion surface has to correspond to the matt side of the focussing screen, the only practical way to ensure that is to put the kit on a collimator and compare the extension differences.
I hardly think there's a need for a spacer as the SMS (single metal slides) used at the time has a big distance between the mating surface and the emulsion surface. Anyhow, decades ago when I was with a photographica group in the UK there were a few people who hacked plastics Polaroid cameras to make Polaroid backs for plate cameras too.