James,
The East Germans and or Russians used whatever parts were available to mix and match to get a functioning pistol.
Also, many of the imported VoPos had the East German "Bull's Eye" plastic grips replaced by the buyers with original wood grips, after they purchased the gun. It's a good probability that this could be the case with yours.
The EG Bull's Eye plastic grips come up for sale on ebay and the gun auction sites quite often. There was a time that you could buy them for $10 or $15. Now they seem to be approaching the $50 mark.
If it were mine, I would buy a set just to keep with the pistol for authentication and originality purposes, before they get too expensive.
And yes, the Crown/U is an East German proof. They manufactured replacement parts on captured equipment. They are also known to have manufactured approx 100 complete Lugers. (see Mark's site) These are very desirable and obviously very rare.
BTW, Mark is very active on the Luger forum's sister forum, the P.38/ PP &PPK forum. He's a great guy and very knowledgable on VoPos. He could possibly give you more information on your Luger.
http://www.p38forum.com/
Ron