To reduce boost if the pulley you wrote about above is on the blower. You need to increase the diameter of the pulley to slow down the blower. A smaller pulley diameter will increase the blower drive shaft speed thus producing more boost.
Ross will make a piston that works with more boost on a special order. Been using them for a very long time at boost levels as high as 23 pounds of boost
in our little stock block Ford flathead V-8 record setting engine's.
Ronnieroadster