SFC's?
 

I recently had an engine rebuild with a few modest tweaks on my 95 Z. Pushing 330 hp. I've noticed a feeling like the back end wanting to come around when I get on it on a straight flat road. I have t-tops and wonder if the car needs SFC's or something to firm up with the added horsepower. Any thoughts?

Nope, nothing to do with chassis flex. These chassis are relatively stiff from the factory. While some will tell you that you "need" them, those people are either trying to make a sale or have not been in a properly suspended car. The main issue is how down right horrible the factory shocks are. When launching the car might feel like its flexing because of the goofy shock valving letting the weight be throw all around uncontrolled like a drunk cheerleader.
Also what about tires? Are you still on the tiny 245 wide stock tires?

SFC's do make excellent jack points however! At least my boxed SLP's do.

Gotta agree with JD though, until your HP gets high enough and your rear sticks properly from a dead launch you aren't likely to need SFCs yet as you aren't likely to twist the chasis.