I know that this thread is pretty much dead, but I did have a little new info. The radiator in my wife's car took a dump recently so I decided to upgrade it since it was going to be replaced anyways. I didn't have the time to do any experimenting with some of the really big radiators from the gen 1&1.5 w-bodies as they do have some small differences. So, I went ahead and got a radiator for a supercharged grand prix which still has a 1" core vs. the 5/8" N/A model. They are identical except for the core thickness so the 1" rad. dropped right in. I did test-fit the fan assembly before installing the radiator to see what modifications, if any, were necessary. The fan assembly has little stand-offs that space it out from the core at the top and bottom, so the 3 bolt locations have a small gap when the shroud is in place. This leaves you with 2 options to get them to fit properly without warping or breaking the fan housing when tightening the bolts. The first option, which is the route I went for simplicity, is to simply place washers between the bolt bosses on the housing and the radiator. If you do place washers in there the 2 bolts that go in the side tanks will not go in so 2 SLIGHTLY longer bolts are required, but it is critical to make sure that the bolts are only long enough to work because if the bolts are too long they will puncture the side tanks and ruin the new radiator. It only took one hardware store style washer per bolt so I only needed 3 washers and 2 bolts to perform the whole upgrade. The second option would be to take a sharp blade or a grinder and shave enough material off of the little stand-offs until all of the bolt bosses sit flush against the radiator and everything will just drop into place with no other modifications or parts. The second option is probably better, but I was very pressed for time so I didn't have the time to do the fitting. Other than that, the bigger radiator is a drop-in replacement. I really find it funny that on autozone's website the supercharged radiator listing has a note in bold letters saying that it will not work to replace the 5/8" core.