Used is used... I would NOT just drop in any used engine. You have no idea how long it's sat outdoors on a rack in a yard, how it was driven or how well it was cared for. If you want it to last plan on rebuilding any engine you drop in.
If temps were high enough to cause the level of damage you're talking about your block and head may have warped beyond serviceability. Look up the specs in the TSRM and measure them.
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