james,
Even with the barrel channel inletted, your plug will not be.
if the barrel is already breached, it's just about putting it in a padded vice, and unscrewing it with a big wrench. If it's never been breached before, you might need some guidance, but its still the same procedure, with a little marking, and filing in between.
My advice........ if you're gonna build guns, you've got to learn to remove a breechplug. If this is going to stop your progress, you're gonna have a bunch more stops along the way to completion.
Please accept this in the spirit given. This is a very basic process you need to know. Do you have all the books for builders.... Those will help tremendously. Don't start with out them.