Over the last year, things started happening to the car to get it back on track.
Immediately it was noticed that the turbo wasn't spooling at all. Out it came for rebuild. Discovered the boost line was completely rotten (crumbled when touched) and the E-clip on the wastegate rod was missing so the wastegate was stuck wide open.
Next was trying to get the engine running halfway decent. I tried many things, before finally determining that the injection pump had major problems. You can follow the saga in the 2 threads I had running at the time:
http://www.peachparts.com/shopforum/diesel-discussion/378230-1986-300sdl-shake-rattle-miss.html
http://www.peachparts.com/shopforum/diesel-discussion/380964-300sdl-ip-issues.html
In the interim, the head was pulled for inspection and to have new valve guides and seals installed. Head is the original #14 head and checked straight (no warpage) and showed no cracks. The engine wasn't consuming coolant or pressurizing the cooling system prior to head removal (and still doesn't to this day).
While the head was off, the tappets were disassembled and cleaned/refurbed and the chain tensioner got the same treatment. They were all gummed up with goop and needed it desperately. I'm happy to say that my tappets are all still quiet as a mouse.