Air Conditioner install
 

I recently purchased a 1964 Pontiac Catalina, Convertible W/389. I am ordering an a/c unit from Southern Air, but pulleys aren't part of the kit. I have a 2 pulley system with one driving the power steering and the second the alt. Does anyone have an idea how to add a third pulley to the lower harmonic balancer to drive the a/c unit.?