The Nikon back is probably a pin registering device which cost mucho dollars back in the day: you could precisely place items and masks to make overlays. Usually in conjunction with pin register slide holders and high end A-V projectors. The polaroid lens is probably from an MP4 copy camera and sometimes prized by view camera buffs or Polaroid buffs. Anything marketed by SAKAR is a piece of crap. The small lens is an enlarging lens and probably worth $10. Use the camera as is. Well done at the yard sale
David