When I move a game in a vehicle I can't stand it up in, I usually go for the back, but some cabs like Tron/Gorf have a monitor protrusion that you can't lay the cab on. I've moved one of them on it's side- I just made sure to lay down a nice sheet of cardboard under it so the sideart wouldn't get scratched up.
Also watch for any protrusions from whichever side you lay it on- a backdoor padlock can scratch the heck out of whatever vehicle you slide it into. Ditto for any protrusions from the floor of the vehicle that can scratch your cab- hatchback latch (one scratched a cab for me once), extra seat mounting bolts/brackets, etc.