Sorry I didnt catch this post earlier TommyGloves, the GXP doesnt share much with the other Bonnies including the suspension so I'm not in here much. Alot of people here assume the GXP is the same as the other models except for the drive train but it is so much different through out. The GXP has the suspension package desination FE5 It is exclusive to the GXP. No other GM model carries this package.
I did alot of research on the suspension before I shelled out almost $3k to change it
The following description I got when I inquired on th net ( way before this when I was considering upgrading what I had), is straight from Kurt Fisher. He was the GXP Program Engineering manager at GM.
Advanced suspension components are custom engineered for the Bonneville GXP, the suspension system more closely resembles a Le Mans racer than a production vehicle. More than 1,000 hours were spent modeling, testing and refining the balance of the components to create a superior ride with a true performance feel.
Structural rigidity was increased through the use of a tower-to-tower brace and a specially dampened engine cradle mounting package. Performance-tuned DeCarbon monotube dampeners, progressive spring rates and large diameter (30-mm front, 22-mm rear) stabilizer bars allow the Bonneville GXP to provide both excellent driver feedback and a smooth, compliant ride.
We really put a lot of work into making the Bonneville GXP perform like a sports car but handle like a premium touring sedan. You can drive it aggressively, it'* made to handle the twists and turns of the road.
With the differences in drive train, exhaust system, brake system, PCM, ignition, CAI, suspension system, wireing harnesses, nose, and body styling attachments it is Not just another trim level.
All this said though, if you are handy and have a cheap GXP suspension to be had and want a project. I would check and measure bolt holes and spring mounts et al.
And decide for yourself if it can be done. I like uncharted territory and will be glad to help if it looks like a go. I have almost my entire OEM suspension sitting on shelves so i know my way around it pretty well now