Agreed. Alot of black smoke without any boost to go with it means quite hot EGTs.
As for not being able to kill a diesel, I don't know if that's completely true since alot of people that play with them have killed them!
This yanmar is no exception. Talking with PPE performance they told me that fueling this engine past their reccomended specs (with turbo) can cause these engines to throw a rod. They didn't say weather or not they had the first hand experience, but I assume they found out just how much the little engine could take the hard way.
If you figure that the factory engine made 24 hp, and if you get the reccomended 5-10 hp PPE claims, then you're talking about a 20-40% improvment in power. I don't know many engines that can make more power than that reliably.
As for clutch upgrades, I talked with Dale at DDP about half a year ago, and he was in the process of seeing if he could upgrade the clutch. the few times I called him back he still hadn't made any progress on it.