I spoke to the Guru at my LHS and he said 4 strokes do just fine inverted. Apparently, the pressure inside the crank blows the oil out no matter what postition it is in.
By the way the same Guru gave me the idea of gettinga Saito Gloden Knight .72 and mounting it in the correct oreintation with the Gold valve covers exposed. That would look pretty cool.
I know you are thinking this Guru is looking to make money, yep, your right, but he has plenty of information for free and his prices are very competitive. Besides, he is one heck of a nice guy.