Exhaust in radiator

Oh boy! That's a tough question. Any time an engine is run hot untill it stops there is a real chance that major damage has been done due to overheating. If the car is in good shape otherwise it is probably worth fixing. However it may be more economical to find a good used engine. If you are willing to invest the time and effort I would first do a cylinder leak down test or at least a compression test and wright down the results. If you aren't sure what the results mean I can elaborate more on that later before you go any further.If the test results look decent then remove the cylinder head. Check the cylinder head for cracks and warpage ( I'm sure it will at least need to be planed and depending on the results of the previouse tests you may want to at least touch up the valves and make sure the valve guides and valve stems have not gaulded). Also check the block for warpage and inspect the cylinder walls for scratches and signs of aluminum stuck to the walls as this would indicate the pistons had siezed to the cylinders. If thats the case you'll either need to tear it down for a complete rebuild or replace the engine.