Running inverted won't help an engine but it won't kill it either. We had a tractor that ran all the fuel out of the dual fuel filters before it stopped, probably 45 minutes upside down at 1800 RPM and no damage to the engine. The sheet metal was messed up, as expected but the engine was still good to go. We tore it down and found that the cylinder hone marks were still fresh as they are new, even though it had 1000 hours on it.
The real problem with a true inversion would be that they would need 360 degree fuel pickups or it will get air in the lines during the inversion. Once you get the fuel run through the filters, you would get a slug of air to get out of the fuel lines and that could take some cranking. In craft that expect knockdowns or inverted flights, they have a weighted end on the fuel pickup with flexible hose so the weight will follow the fuel, and keep air out of the lines. One would wonder if they thought of that.
Thunder Child was in Fort Lauderdale International Boat Show, and was ahead of Kadey Krogen, If I remember correctly... May be a sturdy boat but not easy on the eyes.