So what is a boxlock toplever Army Navy .500 bpe version worth?

Would need more info / pictures.

Are Lyon and Lyon as good as Army Navy?????

Well look at it this way, most Army / Navy's I see
are Webley's. Alot of Lyon and Lyon's I see are Webley's and / or other good makers (I think Lyon used whoever).

If you remove the name, then it is a Webley gun so in answer to your question, YES.

A mate had a ripper Lyon & Lyon 450/400 -one of the nicest 450/400's I'd seen.

FYI and IMHO, it is the US market that was so caught up on "names" that it took them quite a while to realise that Army / Navy, Lyon etc al were just as good as Jeffrey and others.

Just my HO.