Yes, poly bushings will definitely stop deflection. Aluminum will also, but it will transfer too much road noise to the body, and you'll get tired of that quickly!
I put poly bushings in my front control arms, body bushings, and rear spring bushings, and it really stiffened the suspension up on my '71 Camaro. I also added HD swaybars front and rear, lowering springs all around, and Lakewood ladder bars in the rear. It handles like a slot car after that.