Hi Scorpius, The advice given above is both sage and wise! And is, without a doubt, the smart way to go.. But, having said that, there is a small group here on the forum that just can't, and most times won't, leave a mismatched or common luger alone.. I happen to be one of those guys..
... But, building one from scratch out of loose parts successfully, most times comes at the extreme experience end of the learning curve, not so much in the beginning. The AR experience has left us with a whole generation of young gun enthusiasts that can and will build their own, and have considerable success doing so. Well, the Luger is not in that build group for instant success... I would still recommend that you try to build, whether you succeed or fail? As the knowledge gained will far offset the cost of a few old Luger parts... In other words, you'll get real smart, real fast in this game...
... Best to you, til...lat'r....GT ...
BTW, I sell parts, as well as Luger Doc, and Eugene, (Lugerman) ... good luck!