I usually don't bother to remove the oil pan first. There's about a 50/50 chance of creating leaks from an improperly-installed pan gasket, plus the whole point of doing the engine flush is to save time and effort. If it's necessary to do an engine rebuild after flushing the gunk out, dropping and reinstalling the pan would be a wasted effort anyway. Other solvents like kerosene or #2 heating oil could be used instead of Diesel fuel, but Diesel is handy and relatively inexpensive. It's also got enough of an oil base to provide a little lubrication as well as being a solvent. It certainly can't be any more detrimental to an old stovebolt engine than some of the water-thin "oil" that is being used in them by people who don't have any common sense! I don't like kerosene because it has a pretty low flash point, not a lot higher than gasoline.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!