No its not..there are quite a few changes done to the FR500C Grand AM cars. The GA cars still use the 3 link rear setup but thats about it. The control arms are different as well as the panhard rod setup. If you go here it lists all the parts to build a FR500C car...
Beyond all this though...the main reason the cars handled so well is the fact they were only 3100lbs vs. the 3900lb GT500. Not to mention the fact the dampers on the car are $6k, very similar to a Moton setup that the M3's use.