your torque will probably suffer if you use a double pumper. its more down the high rpm street. vac secondaries are much better for most street vechicles with auto as it only opens the secondaries when the primaries are nearly at full capacity. this means at low rpm the air speed through the carb is higher, (smaller hole effectively) so torque is much better.

seems like a 750 vac secondary is just wat u need. 600cfm is prob very restricting for a 460 at high rpm

lobster