This NPC back, made by the famous Marty Forcher, holds Polaroid pack film. I don’t know whether currently available offerings from Fuji or others fit.
The solid, well-built and -finished Mamiya spacer attaches to your tripod head, lifting the camera to prevent the downward-protruding back interfering with tripod head design. The pins on either side of the camera attachment screw are spring-loaded and recede under pressure.