The front will be the same ast your 99GT, but its harder to put the rear springs on the IRS car. It took 6 Hours to do my car on a lift, front and back and C/C plate with an alighnment, but there was two of us, and we were familiar with the project.
There is a few different ways to do it, but I have found the best way to do it, is to drop the IRS, one side at a time. The old spring falls out, and you have to kinda jack each side up back into place.
You might wanna do the front yourself and let a shop do the back if it will be cheaper. Although make sure the shop is close, cause you will have a mean rake on the car.