As long as you hold the engine and any left over money until the check clears your safe.
The scam that was, and possibly still is, being used on ebay was the buyer would send a fake cashiers check to the seller. The amount of the cashiers check would be more than the total due. They would usually say they were a broker for someone, and there broker fees were included in the check. They would ask the seller to foward the broker fees to "whoever".
The seller would do this, plus ship off the item they had won, because after all it is a cashiers check, it's guaranteed to be good. NOT!!
Plus the seller now gets to pay there bank fees for a bad check.
As far as shipping something that heavy internationally, I don't have any idea how to go about that.