I've used Marvel, Rislone, and Diesel fuel all with good results in engines over the years, usually in cases of obvious neglect, or chasing the notoriously bad hydraulic lifters in Packards. That being said, I don't think any sort of flush is necessary unless you see signs of a major buildup issue in the engine. All reputable engine oils these days (and most of the cheap ones!) have quite a lot of detergents in them which clean internals quite well without additives. If things look reasonably clean under the filler cap, I'd say keeping up on your oil changes with a good quality oil should do ya fine.
If you feel a bit of cleaning would do it good, run it up nice and hot, dump a few quarts of diesel into her, idle for a few more minutes, then drop the oil nice and hot and really let it drip drain for as long as your patience holds. It goes without saying, I suppose, that new filters should be installed too, since any gunk that gets moved is going right into them.
