I would think the only issue would be where the exhaust mates up to the collector on the GT. Primarily due to the differences in the exhaust itself, of course, you could turbo the GT and that would probably fix your lack of mating up issue. Plus you would gain a few ponies too!
However, I would be interested to know this as well, I'm seriously thinking about ordering a 185 exhaust for my GT when I turbo it using 3SGTE parts.