It is a massive undertaking and time-wise/financially just not worth it... I have a good set of heads for tat 12 valve bottom-end (assuming that it is a 3.0) for you or somebody else to use on another project!
Send me that 24 valve bottom end - we can fix it and keep the 24 valve ehads on it! There are "ways" (unless the crank is in half!) You can email me at [email protected] or call me a 425.941.4747
The coolant passages are different, so unfortunately not. But I wonder how much machining it would take, or if a thicker aluminum head gasket could realign the passages? But then you would be better off just paying for a new 24v block.