I picked up a colt upper and it is a colt m16 a2 light machine gun with bolt and carrier and charging handle and bi-pod and man thats a heavy barrel.
will look nice on my sp1 lower.
everything is new.
think I will put a regular carrier and bolt in it as I do not know if it will even work with the carrier it came with. don't know looks alot different.
can I put any colt bolt and carrier in it without worrying about headspace or is that not really a problem on the ar15s
and what is this thing worth?
 thanks

Sounds like you got a Colt M16A2 LMG upper. It should have no forward assist as it is meant to fire from an open bolt. The gas tube is built diferently and is much heavier. Also the barrel is a very heavy Hbar configuration. You will need on offset pin adapter to mate to your SP-1 lower.

You can use any carrier assy in the LMG upper, it wont matter. Just as long as it is an AR15 carrier an not an M16 carrier.

What are they worth? Anywhere from $900 to $1200 depending on condition. HTH

Compare your bolt carrier to the pictures in this article...

www.ar15.com/articles/article.html?article=31

...and if it's a M16 bolt carrier, get rid of it and use a AR15 bolt carrier instead. Having M16 parts in a AR15 is illegal. Assuming your bolt has been properly headspaced to your barrel, you should be able to use it. HTH