Engine flush... Yes or No???

If you don't think the engine is ''sludged up'' very much, then I would run a quart of ATF in it with the next oil change and run it for 200 miles. (with a new filter of course)
ATF has a lot of detergents in it.
If it's sludged up badly, then the safe thing to do is to pull the valve cover and oil pan (slant 6), or the valve covers, oil pan, and intake manifold (V8s) and do a diesel fuel scrub and enima.
It's a really messy process.
Rinse and spray where you can to flush the crap out that is missed with brake clean and it'll be pretty good.
Then run the engine with fresh oil and 1 quart of ATF for 200 miles and change the oil again.
It should be good then.
It worked for me and the 360 in my Dart Sport.
It was badly sludged up, but now it's as clean as Kleenex..........