Hi and welcome to the board.
You have a good start and a decent shooting luger.
I would not have worried about the side plate, unless you got quite lucky, you paid a lot for it!
It may have the matching number but it won't be a "matching side plate", as the finish is likely not to match and the inside numbers won't either- unless you really won the lottery!
I didn't know about the inside numbers until today, they will be the first two digits of your serial number or "69". They are located in the spot shown below.
Be also aware that it may not fit correctly or operate the sear without some work- which it sounds like you may already know.
Congrats on your first luger, do report back with how it shoots and how the side plate works out!
Be also very aware that you may not be able to stop with just one luger!
