For anyone who cares...

I removed the lens/shutter ass'y from a Holga 120N, and measured the front-back depth for spacing the lens from the amputated Polaroid camera back.

I measured 1.272" in a couple places (back may not be flat, and there is no pressure plate...I probably have to review this & alter it later after I decide where the film in a Polaroid pack would actually be.