i was thinking you were referring to the plate on the outermost part of the rim that covers the other 5 holes in the rim on the steering axle.
if that's what it is, then it's probably rusted together. good time to "coax" it apart, wire brush, treat rust, and paint. glad ya didn't have to turn the drums. after so many times it's bye bye brake drum (and $$$)
good luck with the project!
