Back in 89, I had a diesel GM Malibu wagon. It had a 350 GM converted into diesel. It was not very good. Head gasket issues, I had to rewire the glow plugs to a manual toggle switch. It was probably the worst vehicle I ever owned. I don't think GM thought through all the issues on that model before they put it on the street.
You weren't alone. The 350 diesel is a far cry from the 6.2/6.5 models. It is honestly an indefensible POS even for the biggest of bad bow tie enthusiasts.
Here's a whole page talking about the head bold problems that plagued this thing. Warning, this isn't safe for life, because it's like a circa 2000 lycos/tripod page with terrible spelling.