The only way to know for sure if springs are needed in the first place, is to install the engine.
If it sits too low or bottoms out over bumps, etc, add spring rate. In my experience, "correct for the application" OEM springs always sit too high for my taste anyway. I'd look into an aftermarket spring, if new springs are decided on.
If OEM springs are used, you could use Pontiac Firebird Formula/TA springs intended for WS6 cars, or Camaro Z-28 w/F41, w/a bit cut off the bottom- but this tends to be hit-or-miss, and the spring rate goes up when the springs are cut. But it is an option.