While I personally think an occasional engine flush is a good idea in concept, actually performing one is definitely a tough call. I've heard of people using five straight quarts of kerosene for flushing their engines, but the thought of that procedure always scared me because of the simple difference in viscosities between kerosene and engine oil (regardless of the weight). Kerosene is a great gunk and sludge remover when cleaning engine parts if you have the time to let them soak, and is probably one of the main ingredients in off-the-shelf engine flush treatments, so I could see how it would help to clean out hard to reach places like valve lifter bodies and small oil passages, but I'm personally still hesitant to run an engine for any length of time with anything but oil.

I'm also not sure how the various engine seals would maintain a good seal against the leakage of straight kerosene, or I'd be tempted to just drain the oil when it was time for a change, replace the drain plug, fill the entire engine from drain plug to filler cap with kerosene, then let it soak for awhile rather than actually run the engine and risk any bearing to bearing contact because the viscosity of the kerosene didn't provide the same sheer resistance per film thickness of a good engine oil.

Maybe that would be a good experimentation suggestion for something like Hot Rodder Magazine?