I have a brand new Bushmaster upper that I bought from a board member that did not come with a B/BC, I also have a brand new Bolt and Bolt Carrier.  

Since these items are both brand new do I need to worry about checking headspace?

I have just built a bushmaster 16" dissapator and a seperate 20" barrel,the bushmaster sales said their barrels are headspaced and ready to go.I had no problem when I test fired the rifle when i had assembled it.In the bushmaster catalog it says you can buy an upper without the bolt and charging handle if you already have one.This is on my own personal experiance, not expert advise though.

Since the bolt and bolt carrier (which has nothing to do with headspace) are both new, put them together and go shooting.  No, you will not kaboom even if the headspace is off a hair.

Just to clarify your statement -

...the bolt (which DOES affect headspace) and bolt carrier (which has nothing to do with headspace)...

That is correct.  Thanks for clarifying that point.