If you didn't drill straight you could have likely drilled a coolant passage or oil passage. I hope you didn't aim the drill bit and slip downwards and drill the block.

Most likely you did wreck the head, that's fixable not the block. Heads are not always easy to find, but that may be you're only option.

broken or stuck glow plugs are best removed by machinist not drills. they won't destroy the threads like a drill.

Most likely the other guy didn't heat up the engine properly to remove them. they are a SOB but can't be done with time and patience.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k