Picked up a cheap vintage bike, and I'm getting it ready for a family member to ride. I want to put a different stem/handlebars; but I'm unable to back out the quill to remove the stem. In checking out the bike how it fits to the fork/frame I saw these notched parts I believe that lock the fork into place. Any idea how to remove, is there a special tool we should use?
There should be an allen bolt at the top of the stem. Assuming you have loosened that but the stem is stuck, you may need to give the bolt a whack with a hammer to loosen the wedge bolt that holds the stem in place. Hold a scrap of wood on top of the stem to avoid damaging the bolt. If it's really bad, you may need to drip some liquid wrench in there.
I'm pretty sure those notches provide a wrenching surface for tightening the headset. Which does lock the fork into place, but that's completely separate from this task.
From Park Tools