For something like this i would stick to known companies like Toll, Startrack, Fastway etc, never had any problems with them. Also good old Australia Post is great too. Yeah it migth cost a bit more to break up into smaller parcels but they are reliable. Ive never had a issue with Australia Post and i have sent and recieved hundreds or parcels withe them. For motors, just take the top end off and send in separate parcel and drain gear box oil on bottom end and take off carby and magneto and send it separate parcels. That will work if its a 2 stroke but for a heavier 4 stroke you would need to take off more bits like the clutch etc