What engine? The best thing to do is find a diagram of the engine.
Maybe wait for a reply from someone that does know what the engine looks like inside before trying anything below.
I think you are right. Those do look pressed on. There might be a C clip inside the engine. Those gears might be a seperate shaft from the crankshaft similar to a camshaft.
I am not sure what that engine looks like inside. I would pull the 4 bolts on that plate and see what is on the other side. Don't be too rough with it, I don't want you to break anything expensive!