many moon ago I worked for a place that flew bank checks and other high priority papers around.
we were told and checkridden using a procedure called: Stage Cooling. We were to reduce the manifold pressure one inch perthousand feet of descent, timed to arrive at the outermarker at approach power setting. ( lycoming engines on pipers)
now, in real practice sometimes it worked, sometimes it didn't...and many times we had to deal with the controllers strike in the USA and had to scud run (legally) using our wits. AND THAT MEANT cutting to idle and spiraling down through a big hole to a small airport or vice versa.
do your best, be nice to your engine and it will be nice to you...but you gotta fly it the way you see it and you can't SAVE the engine and lose the plane and pilot.