What do you mean by overheating? Is the temperature guage pegged? is the header glowing?
I would check to make sure you do not have a blown head gasket. If the car is overheating and has no power it is likely a blown head gasket. It can also be inproper cam timing.
Question. Does the motor not rev abover a certain rpm even at idle?
My first guess would be head gasket though. So inspect the oil and coolant and do a compression check.
Eric
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