LMT MARS L lower
BCM BFH CHF ELW MCMR Mlok 14.5" upper
Pinned and welded A2X or w.e you like
LaRue MBT trigger
Magpul MBUS PRO irons
CMMG lower parts kit
Aero or BCM buffer tube assembly
Grip and stock to taste
You'll want a good optic on there too. A 1-6x or 1-4x LPVO would be a solid call. Sling, mags ammo etc. God speed.
That would be a sort of build. You would build the lower, but slap the upper on. Are you wanted a done factory rifle?