You can put an SR20DE throttle body on a GA16DE intake manifold. You'll have to port the intake manifold, put a vacuum tube on, and swap the TPS's and do a little throttle cable jury rigging, but it can be done. You could even try putting an SR20DE intake manifold on as well, might have to port the head though. If you scroll down to the 4th picture in this article, you can read the paragraph that I got this info from. http://www.nissanperformancemag.com/april99/mather.shtml
It's a good article about what the GA16DE is capable of. Granted this guy knows his shit as well or better than our resident heros Mike Kojima and Andreas Miko.