Jim
The chassis is the same. The GTI would have 1.8L engine, 5 speed trans (most Rabbits had a 4 speed), vented rotors, and different springs and sway bars. Not a "plain" Rabbit by any means.
For it to be a "legal" ITC chassis you would have to wait for the VIN rule to be passed.
Or you could swap all the VIN numbers from the old chassis to the new.

Good Luck.

Dave Parker
WDCR HP #97
2007 MARRS HP Champion