Hello I will answer your question,
The OCV is the oil control valve which is mounted to the end of the camshaft and allows the camshaft to be rotated slightly to changr the valve timing for more power and betteer fuel mileage. The engine should start but will not run properly with this setup so I suspect that something else is inhibiting the engine from starting.
Why was the engine replaced? Did it overheat?
Yes there was a major redesign in the head to meet emissin standards. If you replace the head with an 03 it will work with the short block but you may be better off trading the engine for the correct year as it is most likely more expensive replacing the head.
Sorry for the bad news but give your mechanic this website: hmaservice.com
It is free to use and will give him access to factory level information.
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