I installed it on my 78Z and saw a good power increase, it use to stop pullings at about 5600 rpm now it pulls hard thru 6500 rpm's. I would say get it by all means, however I do have other mods on the Z. Hope this helps.
I installed one on mine while I was going through the motor. I am of the opinion that this is NOT a bolt on upgrade since it involves some work to the intake manifold.
The opening in the intake is sized to match the stock TB, so to gain anything out of the larger one, you will need to open the intake manifold up to the size of the new TB. Not something that would be easy or advisable with the intake on the car.