You don't need to ship the whole motor just the cylinder, piston & head...right?
It's right about 15 LBS and should fit in to a 12x12x8 if you pack it REAL GOOD with lots tightly wadded up newspaper.
There is also the option of using APO/FPO/DPO which is mailing through the united states mail system to a military base, which I know exist in Germany.
https://www.usps.com/ship/priority-mail-flat.htmNot sure if you need to be stationed at the base or how it works but I know any base is considered US soil and the US postal service will deliver & ship from there.
Any forum members that have served might be able to give you more info on this?