Here's a few pics showing the locking tabs front and rear.
The rear ones are like little boxes in the 2 corners and the plastic cover slides forward over the back of the head and hooks around the case. The front then drops down over the head and has 2 small little 1/8" wedges that slide down over the front of the head and snap into place to lock the front down. They are about 5/8" back from the front. If you warm it up in hot water, you can then insert a feeler gauge down over the wedge and gently work the head up by lifting one side and then the other. Once it lifts up a bit you can slide it back to release the rear boxes.
Be careful not to pry too much as the plastic can break when brittle.
