G'day Jim,
The main problem with running engines inverted, is tank height, the centre line of the tank MUST be level with or no more than 3/8 (10mm) below, the main needle valve, or fuel nipple.
The engine does not care which way it is facing, as long as it is properly run in, & tuned.
Check out this site for (1) prop sizes,
http://saito-engines.info/prop_sizes.html
And (2) throttle setup & tuning,
http://saito-engines.info/throttle_setup.html
Valuable info.