Can you mix NEW uppers and NEW bolt setups without doing any headspacing and just shooting? I am looking at an new LMT  upper. Can I get an upper from one place and if they don't have the LMT enhanced bolt group can I get it from another place and just assemble and shoot?
Or can you use an enhanced RRA bolt in the LMT.  THANKS in advance

Quoted: Can you mix NEW uppers and NEW bolt setups without doing any headspacing and just shooting?

YES.  While it is never a bad idea to headspace a bolt to a barrel.... as long as they are made to spec, they will headspace just fine.  I would venture that the majority of us who build our own just buy them and shoot.

I am looking at an new LMT  upper. Can I get an upper from one place and if they don't have the LMT enhanced bolt group can I get it from another place and just assemble and shoot?

Yes.  The only risk is that the barrel extension or bolt (or both) would be out of spec.  I personally have never experienced this, or read about it, but I am sure it is possible.  Would not cause me any concern.

Or can you use an enhanced RRA bolt in the LMT.  THANKS in advance

You can use any bolt with it.

I would not worry too much-but I'd check the final product with the correct gage!  It never hurts to verify that the headspace is correct.

Can you mix NEW uppers and NEW bolt setups without doing any headspacing and just shooting?

Yes.  Never have seen a problem with new parts.