In general, it is not feasible to put just any other bike engine into a Harley Davidson frame without making significant modifications to the bike. Harley Davidson motorcycles have unique frames and engine mounting systems that are designed to accommodate their specific engines.
The engine mounting points, dimensions, and configurations of different motorcycle engines vary widely across brands and models. These differences make it difficult to simply drop in a different engine without modifying the frame, engine mounts, electrical system, exhaust, and other components.
Moreover, the overall design and engineering of a motorcycle are interconnected, with the frame, suspension, brakes, and other components all working together to ensure proper performance and handling. Introducing a different engine into a frame that was not designed for it could result in imbalances, compromised handling, and safety issues.
If you're interested in modifying a Harley Davidson motorcycle with a different engine, it would typically require significant custom fabrication and engineering work to ensure compatibility, structural integrity, and safe operation. It's advisable to consult with professional custom bike builders or motorcycle engineering experts who can provide guidance and assistance in such projects.