440 Vacuum Leak, where to start?

Carby? That makes it sound all warm and fuzzy. Performance carburetors are supposed to be mean and nasty and suck your HEAD in if you get too close. "Carby" just doesn't sound right. On to your problem. Whistling sounds are always always ALWAYS at the joint where the carby (or spacer in this case) joins the intake manifold. Simple to locate. Get you a spray bottle full of water and while idling, spray all about the carby base and around the spacer plate where they bolt together and where the spacer plate bolts to the intakey. When you hear a difference in idle speed, you found your vacuum leaky. Since the torqueflites have no vacuum assist, I fail to see how the transmission could be involved. Keep us posted.