If you are doing this for someone else, I would stop immediately and do nothing else. You are about to pay a princely sum for a worthless rifle after the action is ruined attempting to remove the old barrel.
If you ignore Rule No. 1, get a very thorough release.
Regardless of who the gun belongs to, it sounds to me like the un-installed barrel may be worth more than the completed rifle, even assuming that the action survives removal of the old barrel.