Thanks for considering our chassis for your build!
We can do the chassis for the Chevelle of the GTO. (A few differences in the chassis for the GTO, but we do offer them as well)
My only comments would be that the earlier cars (64-65) are narrower and you can not get as wide of a front tire under them. Not a big deal for a street car, but if you are planning to aggressively track the car, more rubber is always better. The GTO would definitely be more unique, but parts could be harder to find and more expensive as far as trim pieces go.