if you triple the size of the drive pulley, then you are tripling the belt speed. get enough belt speed, and you cannot keep a belt on the pulleys.
i tried to build a supercharger for a snowmobile. had BIG problems with the belt speed.
FWIW.
again, if you are scared to mount two turbo chargers SOMEWHERE in the engine compartment, then you probably should be nervous about mounting an even larger supercharger where belts and stuff will get to it.
supercharger, particularly the centrifical type you are contemplating, pump air a a function of the square of the RPM. this means you would relatively little air at lower rpms.
turbos, OTOH, function more as a function of throttle position. give it more throttle, it gets more fuel, which prodcues more heat, which produces more boost.
kind of hard to argue with that logic for a pickup truck.
for drag racing, positive displacement blowrs make the most sense IMO>