Grant, do you think that the OP could substitute that 5.5 HP motor
with a 3 HP motor and a smaller pulley?

i

Sure. You just get 3/5 as much air, that's all. In fact, I still have
the 3HP 3-phase motor and the smaller pulley that came to me on *my*
Quincy. Running the air pump slower also means quieter and longer lived,
so it isn't all bad. - GWE