One thing though: The GZE has a lot of low end torque, because it's got the SC12 on it. The 20Vs have a lot of high end torque because they've got the 5th valve and high compression. Just like Honda's B16s do. So by using the GZE shortblock, you've just removed the high compression part. Making it very difficult for the cam timing to do its job. This in essence should probably kill your top end.
Then we come to the problem with using the SC12. Even on a stock GZE, you will notice that the engine pretty much runs out of steam at high revs. This is because the roots design of the SC12 causes it to become very inefficient at about 4-5k rpm. Now, having boost might allevieate the problems of low compression killing your top end power, but the intake charge at that point is VERY hot, even after the I/C. This may cause pinging, or other problems with your engine.
Now for the physical problems with doing it. What Toyotaspeed90 means when he says the intake manifold won't fit, is exactly that. It phsyically won't mate up with the intake ports on the head. You won't be able to use the 20v intake manifold with the ITBs either, because the GZE setup goes TB -> SC -> IM. It makes it next to impossible to use that setup on the GZE, since part of the SC12's mounting bracket is part of the intake manifold. Now, I know that for engines where the TB is attatched directly to the IM, you can get or make IMs for relatively cheap. However, since the IM for the SC12 feeds downwards from the I/C, and has brackets for the S/C, and possibly also the pipe for the TB (I'm not going outside to check, it's 3:30am), that's going to be one damn expensive manifold.
And is there even an affordable aftermarket system that will handle VVT-i?
edit: so okay, it was several things.