Unfortunately, the gauge of the wire inside the transformer was too large to use for a guitar pickup, but it still is good enough for an electromagnet or whatnot.
Step 1: Tools.
1 pair of needlenose pliers
1 can of industrial strength repetitive task preparedness
Step 2: Assess the Situation
I immediately noticed that the entire thing was encased in a resin-like shell to protect it and hold the darn thing together.
Step 3: Begin
On the top, take your trusty pair of needlenose pliers and insert them into one of the corner screw holes and pry one corner up.
Putting the whole it and kaboodle in a vice will hold the project steady.
From your loosened corner, crack the resin shell and laminating material between the layers of steel by lifting up and sliding along the crack on the sides.
The first layer is the hardest to remove, mostly due to the layer of resin that holds it to the wire coils and other layers.
Step 4: Remove Keeper
Step 5: Do It Again
Then do it again.
Step 6: Done
Now, unwind the tape, cut off the solder and other odds and ends, and wind onto your next project.