Yeah, that's fine. I've moved all my games on their backs in a minivan. Just, before you move it, check that everything is bolted in the way it's supposed to be (monitor, power supply, boardset, transformer, etc). If everything is secured properly, there will be no problems.
Also, when you get it where you're going, take the back off again and look to make sure everything is still where it's supposed to be, and that no junk has fallen onto the boards or power supply. Last thing you need is a stray quarter shorting out the fuse block!
-Ian