One other consideration you might want to take is that a serial hybrid will probably get the same mileage as a conventional car. You are essentially replacing a mechanical transmission with an equally inefficient electric one.
The only way you'll get ahead is if you downsize your engine and run it constantly at its max BSFC. To do so, you'll need a battery or ultracapacitor bank to soak up the fluctuations in the driving cycle.
Rather than run a bank of alternators, you'll gain efficiency by driving a single motor directly. You'll also gain efficiency by running a single motor on the rear differential rather than two. A direct attachment to an OEM differential probably won't work as most advanced motors will require a reduction of 6:1 (~12000rpm redline).
A centrifugal clutch is meaningless on a motor because it stops spinning at a stop...unless you're running a funky, old constant-speed AC motor.
I hope I don't sound like I'm knocking down your idea. I'm just trying to make sure you start walking in the right direction.
- LostCause