You have to take off the top nut and straighten the locking plate and take off the bottom nut. Then you use a screwdriver or pry bar to pop the bottom plate off the steering stem. You are right about it being in one piece. The only way it comes off is to spring it.
I made an 8 point wrench for the big nut out of a hole saw blade. I used a 1 1/2" hole saw, ground off the teeth, then heated it to cherry red and hammered the end into the 8 point hex shape using a piece of steel in the vise as an anvil. Then I used a 1/2" breaker bar in the mounting hole to drive it.
Hope this helps,