i have shipped many motors of all sizes and shapes, i think it is best to help the customer out and myself by keeping the shipping to a minimum.

start by draining any fluids from the motor, this way when the shipper tips it over you wont be charged for a cleanup or haz-mat spill (you can be fined in excess of 50,000 dollars for causing a haz-mat situation in a federal building and the post office counts as a federal institution).   after draining, fid any pokey or sharp parts of enhine that may tear packaging and cover them with a little piece of card board and tape it down. now buy a cheap roll of saran wrap at any dollar store and wrap the motor. go nutz use all of it if you want. doing this will ensure any other oil wont leak out . 

engines up to 70 lbs. 

i have found   that the cheapes and easiest way to ship a small motor is  using a chap rubbermaid style tote or bin. place engine inside pack with dense material like old rags foam or tight packed paper, then duct tape the lid closed wrapping several times, and your ready to ship. 

engines over 70 lbs.

get a piece of  plywood cut to roughly 8 inches wider than the motor, attatch three 2x4's to bottom of plywood spaced evenly one along each edge and in the middle. then  drill 4 holes on each corner, set saran wrapped motor on top and secure with ratchet straps utilizing the drilled holes for mounts.   i have not found a frieght shipper that didnt accept this style of  open crating.