Yeah, the engine, fuel, and electrical systems are all part of what makes up the AFM, and as such currently have to be done from scratch. There is no AFM SDK available.
While it is true that the electrical system (AC) is dependent on the engine, so are several other systems. In reality, all you need is the data (RPM) out of the engine to make the AC electrical generator work. This wouldn't need to be incorporated in the same AFM dll.