Machines are designed to have the head box folded down, legs off and stood on their bum.  You are trying to avoid any damage anywhere but especially where it can be seen.  If it is on it's belly, good chance it will get dragged at some stage and you risk cracking or splitting the ply on the bottom of the cabinet.  The machine takes up more room if it is on it's belly you may get charged extra for the transporting.

You want plenty of padding between the top of the cabinet and head box in order to minimise any dents in the side rails.  This should also restrict any movement in the backglass/translite and also protect it.

Cardboard around the machine as Wotto mentioned.  Do not use packing tape to tape the head box to the cabinet, it is a pain in the arse to remove and may well do a bit of damage when you try to peel it off.  The best thing is the industrial cling wrap.....wrap it around the machine two or three times and it holds everything together very nicely and peels off without leaving a trace it was ever there.  Legs can be wrapped in cardboard or the plastic and then wrapped onto the machine somewhere.

There are different ways of doing it, but I would be happy to see a machine turn up like this if it was mine.