When I built my POF lower, I went Bushmaster lower parts kit,...yes they all work, FWIW, the single stage trigger is damn crisp. for only a couple bucks more than a standard lower parts kit.
Please consider a free float barrel and not the Delta Ring,....so many more options depending on your application.
The wonderful part of a build is being a brand whore....Miculek or Titan Comp. rails, Bravo Company BCG, Larue Tactical Firing Pin, Get the M4 feed ramps, Mil-Spec not Commercial, choose your barrel, (I went Colt HBAR Heavy), Unless your making an AR for anything other than it was designed for, it is the Barbie for guys....
If it's just a beater, get the DPMS Lower kit, choose an upper, (I prefer a flat-top) and roll.....Easy enough to make it happen.
OBTW, When are you leaving Kalifornia?