Difference in shaving horse, dumb-head, and shaving mule?

i have been scouring the internet trying to find an exceptional set of plans to build a shaving horse, when i came across a little blurb about a shaving mule, which said that a shaving mule is a hybrid of the european shaving horse and the asian dumb-head. What are the differences, pros and cons to each. Also, any good resources on where to find plans would be greatly appreciated. Thanks.