I have used a Saito 150 in the inverted position many times and constantly had problems with getting the engine to idle. In fact one of the other guys in my club was having the same problems I was having with a 180. Another member kept insisting that we both get a Perry fuel pump and that our problems would be over.
I and the guy both kept having problems until I finally got the perry pump. Guess what, Problems solved. We both now use the Perry pump, and have had absolutely no problems since. I guess we are never too old to learn. Go ahead, invert the engine (with a Perry Pump), and have a great time enjoying your airplane and the power that the Saito can produce. You will love it.