Yeah, you can re-use everything. The extractor pin is solid and easy to remove, just press the extractor in by hand and push the pin out with a punch. The ejector is a little more trouble, it's a tiny roll pin, but not a big deal if you have the right punch. Definitely strip the bolt down for this job.
You don't need the bolt in the carrier to check clearance, just the stripped bolt by itself is all you need. You're checking the distance between the barrel extension lugs and barrel face, nothing to do with the carrier.
