If you are increasing the volume of what is to be compressed, and push it into the same small area in the head, how does that lower the compression? More stroke or more bore pushed into the same area will raise the compression. Then do you have to re calibrate injectors, remap the computer etc?
The thing that troubles me about advising someone to buy a high mileage diesel is they get it, go down the road and something happens, maybe throw a rod. Being miles from home they tow it to a shop that tells them that diesel repair is going to cost them six grand, maybe more.
Odds of a failure? I really don't know, but someone considering an out of warranty diesel needs to know it can cost 4 times or more to repair a diesel if something does go wrong. Most situations have advantages and disadvantages, so I just don't want prospective buyers to believe they will buy a diesel with 200,000 miles on it and live happily ever after. They will have lots of power, good fuel economy, and then they are blindsided with a high dollar repair that they may not be able to afford. My buddy has a Ford 6.0 diesel. I could buy a nice truck for what he has spent on that engine.
I like the story about the King who has no clothes. Just because "everybody" says something is great, doesn't make it so.