Charles,
A call to Mike Elias at Metric should reveal his best experiences for shipping engines in and out, including the do's and don'ts. Remember, with the exception of the local trade every engine he rebuilds has to come in and go out, usually by truck. He's been doing this for so long, he'll tell you what works and what does not.
While you can "strap it to a skid", I'd prefer something a bit more protective; that is, a crate. I've made plenty of them and also had them made when I was in the computer business. While it used to be pretty cheap, that was when a 2x4 was $2 and a sheet of 7/16" OSB was $7.50. Times have changed. I'd still build a crate. Your engine is worth quite a bit of money, and even more once rebuilt, so the best protection is a proper crate. They are pretty easy to build with simple tools. There are these devices you can place inside the crate called a "Tip and Tell" as well as a "Shockwatch"; they will tell you upon arrival (the recipient has to know to check their status upon arrival) whether the freight was mishandled.
I once had a 3,000 pound laser plotter crated in Berlin and shipped to Minneapolis. It had fallen over and was damaged. I did not have these devices in the crate, but the two forklift holes in the middle of one of the sides of the crate was all that the Delta Airlines Freight adjuster needed to see before they issued us a full refund.
Even some strapping supplies and materials are not that costly these days with Amazon. And yes, I'd protect said engine with shrink wrap which is essentially oversized rolls of Saran Wrap or something quite close; it's PE film.
Once you get the engine in the crate or skid, you need reasonably precise measurements/dimensions, as well as weight. Be sure you have the ability to get that.
You generally won't take your crate or "engine on a skid" to the post office or UPS; it will go by truck. More specifically, what is called in the industry LTL (less than load) freight. Yes you can use freight quote or you can go direct to one of the major and reliable carriers, such as R&L, ABF Freight, Old Dominion, etc. Most of the LTL shippers expect to pickup at a commercial (non-residential) location. Sometimes the massive tractor trailers are banned in residential neighborhoods, or simply cannot navigate the streets. Also, and this is fairly important: do you need a lift gate? If you are at a residence, probably yes unless you have hired a few muscle men to lift the engine onto the back of a trailer! If on a commercial loading dock, no lift gate required. This is important since if you need one you'll pay extra, sometimes a charge of up to $125. Moreover just because you request and pay for this doesn't mean that they'll actually show up with one, or one that works. Been there and done that over the decades...
Don't even THINK of sending this out without full insurance; what that means is enough to cover replacement.
You'll be quite happy with the results of Metric Motors. They don't "fix" poorly performing engines; they apply the same consistent set of measurement and rebuilding protocols to all engines, ensuring a consistent product out the door.
