Diesel fuel or kerosene won't hurt the engine, even if it's circulated with the oil while it's running. If any really big chunks get dislodged, they will end up in the oil pan eventually, and the oil pump pickup strainer will keep them from getting recirculated. Diesel is considerably safer than kerosene, since it doesn't make as many flammable vapors when heated up to crankcase temperature.
I like to add about 50% Diesel fuel to clean engine oil (Plain old 30 weight HD is fine for flushing) or maybe go one quart over full, then run the engine at a fast idle for 30 minutes or so. DO NOT DRIVE THE VEHICLE! Drain the oil while it's still hot, and maybe repeat the flush with a fresh fill if the engine is really cruddy.
Once the flushing is done a time or two, remove whatever sheet metal is handy, oil pan, side cover, and valve cover, and use an air-powered siphon gun and more Diesel fuel to blast the loosened crud away. Don't worry about getting aggressive with it- - - -you're not going to hurt anything with air and solvent. Replace the sheet metal parts, with new gaskets, fill it up with oil, and drive on!
Jerry
