What's most important is the carb to tank relationship. The tank should be slightly lower than the centerline of the carb. Inverted engines generally run fine, but they are more prone to a flame-out due to wet fuel landing in the plug. They are also more prone to hydraulic lock if you flood the engine when starting it. None of these things are a big deal if you know what you're doing and you get the engine set up right (mixture controls).

Also, you can use an onboard glow igniter to help keep the plug hot, but usually it's not necessary.