Thanks for your advice in advance.
Ken

Yes you can, as long as your upper and barrel are head spaced correctly.

I do however prefer to use seperate bolt/carrier per each upper. from my limited understanding, the lugs on your bolt will wear into the lug recess area in your barrel extension.  this wear cause the bolt to mate itself the the particular upper it has been shoot in.  If I remember correctly, Marine Corp will number the upper to the bolt carrier for this exact purpose.