If it is running, not missing, or chugging or anything like that...engine is not the issue. I would get it out of there, fix the overheating issues by putting in a stock rad, stock pump, thermo, and stock cap on it. Then run it and see what happens. I would NOT take the advice of some place that just randomly says the engine is bad with no proof. Especially not one of the 4.0 blocks
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