Went ahead tried it came out fairly easy
That's because its never been fired
Had the rifle been fired, you wouldn't get the plug out. With the actual Ultimate rifles, the plugs after firing will wedge and lock the threads. There's not a product on the market that will allow the breech plug to remain removable.
Its actually a 2 piece breech plug. Once it wedges in the barrel, the only way to remove them is to just twist the nipple until it breaks off, then drill the plug. The last process is using a very large EZ-out to remove the threads. Ken Johnston did it intentionally. In the beginning he was afraid that shooters would damage the threads in the barrel. Then the secondary reason was, MONEY. If the breech plugs needed replaced, he made money replacing them. Business 101 LOL
Personally, I'd leave that plug out of the rifle, or at least only a few threads into the barrel. Of course the bolt won't close but, if the next owner of the rifle wants the Arrowhead ignition, then it'll cost him/her the smith's fees to remove the plug as described. You could leave it out, put it in a plastic bag and attach it to the rifle. It would really save time and money for the new owner.
As I mentioned...... that's a great price on the rifle unfired. Good luck on the sale.