Note: This thing's files are identical to the files for the Headcrab Zombie. They are re-posted here for clarity.
Zombie Upper torso.stl needs to be printed with support material. It prints best upside down, with the top of the neck peg resting on the platform.
Use the arms and legs from:
Assembly (Using the images for reference)
Glue the Lungs and Organs into the Chest wound. Then press the upper torso onto the lower torso, and press the finished chest wound into place. Use glue to secure the parts together if needed.
You will also need: