Frank,
Package the engine, double box for protection. Don't go crazy with the size.
Take the box to your local USPS. Just say, "It's going to Australia." They will give you a form, one I believe.
Fill it out then go back up to the counter. You're done, the rest is the post office person.
Be honest about what it is and what it costs. They will say there's tracking, but not really. Almost tracking.
I sent rolled plans to Australia about 6 weeks ago. Took 3 weeks to get delivered.
Good luck.