I spent a few hours on Saturday swapping the radiator out on my brother's Pontiac Grand Prix GTP. Everything went really smoothly. The radiator that I put in a month or so ago was for the naturally aspirated Grand Prix, and the one I swapped in on Saturday should be the correct one. In the picture, you can see pretty clearly the difference between the 5/8" thick core of the NA rad, and the 1" core of the FI rad.
I also did a thorough flush of the cooling system, including a chemical flush and two flushes with a "flush 'n fill kit," replaced the thermostat and radiator cap, and switched the car over from Dex Cool to Peak Global Lifetime. The car is at ~95k miles now, hopefully the cooling system will be good for another 5 years with this work.
Honestly I had originally thought that the Grand Prix was a pain to work on, but the deeper I get into it the more that opinion changes. The radiator was a simple affair once I got over the fact that yes, I had to remove the cross braces, battery, intake, and filter box to get the radiator out. After that, pop the Jiffy-Tite transmission cooler lines off, remove the upper and lower hoses, unbolt the fan shroud, lift the shroud out of it's clips and out of the car, lift the condenser out of it's clips, and the radiator came right out. Installation the reverse of removal.
As a bonus, I got to hoon it just a little on the post-work test drive. Revel as my brother's aftermarket catback and pod filter intake completely blow out the mic on my smartphone.