Parts manual says all Base Firebirds except the four banger had the same front spring, GM part number 14034238, which is discontinued, but should cross to the Moog 5602. The Firebird Trans Am GTA uses the Moog 5662, The TTA is a GTA with an engine option, so that's your spring.
The 5662 is two inches shorter in free length and a specified 0.25" shorter compressed length, so it'll bring the nose of the car down compared to the 5602. It's also substantially stiffer.
i ordered a 5660 to see how that looks on her.... put new sachs struts in it as the old koni's were shot... also put in new rubber strut/spring mounts and new kyb strut perches...or what ever they are called.