Are you sure ETOPS does not apply to freighter flights, only passenger carrying revenue flights? If there were no passengers or revenue freight on board, I agree that FAR Part 91 would apply on this delivery flight.
Any aircraft over ocean with less than 3 engines is required to always be with a FAA set distance from a place to land after the loss of one engine. It detailed in each airline's FAA approved OPS SPECS. You can find more in the FARs...
The last time I flew between SAC and North Island, Lake Tahoe was not along the "direct route". But BZ for the guy who salvaged the water landing. WTF were they thinking?
Naval Aviator long ago
A4, A3