Your biggest challenge is breaking the collar free of the handle. Two opposing strap wrenches are your friend there.After 5-6 years of looking for one, I finally found my first #400! This is a 400-4 picked up today at an antique store that we hadn't planned on going to but ended up there after the flea market we went to ended up being a bust. I haven't restored any of my many vintage brushes yet, so I'll practice up on a few, then tackle this one someday.
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I've redone many of them, get yourself a 24mm knot and have at it!