Depending on the engine, there is a lot of "mass" to it so that "if" it is dropped or mis-handled the potential energy built up from raising it above the floor will be released as kinetic energy.
That energy must go someplace.
Your packing must assume that this item will be dropped at some point.
It must have packing not just to prevent nicks and scuffs, but the packing must be able to absorb ALL the kinetic energy released if dropped. The packaging does this by deforming when impacted. Ideally the if package should show up to it's destination looking all damaged, the packaging will have taken the brunt of the energy and sacrificed itself to protect the contents.
simply putting a bit of bubble wrap around it is nice if you are personally transporting it, but once it leaves your hands, never trust the courier to handle it as you might.
If you cannot strap the engine down to a wood frame of some sort, strap it to a small tyre, then wrap that and box it. The tyre provides a very strong cushion against shock and is flexible. Old used tyres are great for transporting small engines around in vehicles so they don't roll and don't get damaged.
I have sent an Isetta engine to Mexico once and made a wood crate for it. The engine was bolted to the crate and then put inside a sturdy cardboard box with solid slabs of 2" thick styrofoam sheeting surrounding it. It arrived safely despite being delivered to the wrong destination, unpacked and then re-packed.
There is one guy in the USA that works on Isetta engines and he has a couple of wood crates made up for proper shipping. He will ship you the empty crate, you bolt your engine into it and then send it back.
If you are having someone ELSE send you an engine, don't trust they will pack it properly. You might have to make a container for it and send it to them.
I once bought a rear window glass for a bubble window Isetta from someone who said they would not ship it because they could not figure out how to package it. I happened to have a sample piece of glass (very large and unwieldily), made a cardboard box container lined with plenty of styrofoam and sent it to the seller. He just dropped the glass into the box, sealed it up and took it to FedEx after I gave him a little extra money. It arrived safely and eventually went to a friend in Italy in that box.