I cracked a 603 head. And yes it makes a horrible sound like there is zero compression and the starter is under no load. Check turbo compressor and see if coolant is in there. Depending on if/where the head is cracked the strokes will cough coolant back into turbo. (ask me how I know
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Head probably warped/cracked on first overheat, then operating heat took it the rest of the way after serpentine belt was replaced.
Given the fact that it ran after the belt replacement I would guess that the rest of the engine internals, etc. suffered much and therefore a head replacement (if that is what it is) should do the trick.