Did they break off in the head or are they seized? If they're seized I will walk you thru getting them out one by one. There's an extractor tool, if that doesn't work comes to worst you pull the head and have a machine shop extract them out. I've drilled out a plug before tho, it's risky

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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