The main challenge in this swap is the difference in engine size. The GT750 engine is a three-cylinder engine, while the GS550 engine is a four-cylinder engine. This means that the GT750 engine is physically larger and will require some modifications to the GS550 frame to accommodate it.
Another issue that you will need to address is the difference in engine mount locations. The GT750 engine has different engine mount locations than the GS550 engine, so you will need to fabricate custom engine mounts to fit the GT750 engine into the GS550 frame.
Finally, you will need to consider the electrical system. The GT750 engine uses a different electrical system than the GS550 engine, so you will need to either modify the GT750 engine's electrical system to work with the GS550 frame, or you can install an aftermarket electrical system.
Overall, while it is possible to fit a 1977 GT750 engine into a GS550 frame, it is not a direct bolt-on swap and will require some modifications. If you are not confident in your ability to perform these modifications, you may want to consider having a professional mechanic do the work for you.
