DaveO - strictly speaking, the beaver is actually the bottom portion of a knight's helm (I ought to know, I'm a re-enactor) that protects the chin & mouth. It can't be "cocked up" I'm afraid. The beaver is definitely a hat in this case.

Johnny - glad to see yer still wiv us! *g* You can always complete the anecdote with the (possibly) correct definition of "posh" y'know. Even the dikkers don't have this. The OED says that it may be derived from slang for a dandy or fop. So I looked up posh in Partridge's dik of historical slang. It reckons that posh derives from the Romany for half, which was applied to a halfpenny, from there to mean having money in general, and ultimately someone that had (or appeared to have) money was therefore posh. Not quite sure why the main dictionaries don't credit this explanation suficiently to offer it moer assuredly. Possibly because there isn't enough of a concrete trail back to the original...

As to mantle for put together, that one is a back formation I think. Webster Online gives the second definition of dismantle as to strip of dress or covering, & mantle as a cloak or covering, or (as a verb) to cover something; rather than to put something back together. I've also seen mantling used as describing the action of climbing onto a ledge (as in mantlepiece, in this context).