HK416 Parts kit with PRE-Order barrels , bolts and receivers at Brownells

That might change the equation for full 416 uppers if the upper receivers are date stamped and have the magic " hk".

For the lower, consider a LMT Mars-L. It's got the pictograms for a semi auto system and a tricked out ambi- bolt release.
 
Bought the stripped lower receiver from Brownells, but to me the parts kit doesn't make sense. Doesn't even include the barrel - which is basically the point of buying an HK 416 upper vs. MR556. You can buy a complete parts kit (everything but receiver and sights) elsewhere for something like $2,600.