[ShadeTreeMech]

Option 3 is the better, and I can explain why.

Less fabrication, and almost no modification of the vehicle. Simple is sometimes much better, and generally more user friendly.

You have to use the transmission anyway; as you said you can't go around in neutral, BUT you could get most of the benefit of coasting with the engine off with the electric motor in place of a supercharger.

As you likely know, when the vehicle is coasting in gear, the fuel turns off. Breaking that down, your throttle position sensor reads 0, your vehicle is in gear which keeps the crank turning, so the computer turns off the fuel. If you had an electric motor helping to keep the crank turning for longer you would be able to have extended coasts with no fuel being burned, which is equivalent to coating with the engine off.

Since the only scenario where the fuel would go off would be during 0 throttle, a switch could be wired to activate the motor when the throttle is at 0.

Option 3 also means you'll only need a limited rev range for the electric motor, which is right in its ballpark.

And with the correct sized belt, they are capable of handling extreme torque and power. Many industrial motor applications use belts to transmit power, and generally do a great job of it. Somehow I doubt you'll be needing all the power a good belt can transmit.

Obviously there are huge gaping holes in how to do it, but with the EV community alive and well here, I doubt it'll take long to learn what is needed.

Good Luck. I've been thinking about doing the same exact thing myself.