you need a two speed drive for your alternator. When I was an engineer at ford I proposed a drive system like they used 0n the 1957 Thunderbird paxton supercharger. After I left ford they used the system for a while in 84 on the bird to drive the alternator, power steering and ac compressor at higher rpm at low engine idle then switch to low speed on the highway when the engine rpm is up. the accessory speeds would be at normal speed. I made the proposal but have never searched out a car to see how they actually did it.