Can a Vanagon water-boxer engine be replaced with an air-cooled VW engine?

Yes, a Vanagon water-boxer engine can be replaced with an air-cooled VW engine, but it requires significant modifications. The air-cooled engine will need a different mounting system, as well as adjustments to the cooling and exhaust systems. Additionally, the overall performance and driving characteristics will change, so careful consideration should be taken regarding compatibility and intended use. It’s generally more common to replace the water-boxer with another water-cooled engine to maintain the vehicle's original design.