FYI: There is a 90mm GM throttle body that is made by Hitachi (same manufacturer for the Z/G TB). It uses the exact same actuator and sensors, so the opperation is the same, just with more surface area.
The GM part number is 12602800
The pigtail that you will need to adapt the harness is 88988106

We did some testing here with a 90mm intake tube and the above mentioned TB, but the gains we saw were minimal, so we never took the development any further. In the test that we ran it responded really well under load, but it had some pretty bad idle surge. Since we never took it any further, I don't know what it would take to correct the surge, but I'm sure it could be fixed with some tuning.

We also have a couple extra VERY nice CNC adapter plates to fit this TB to a Z/G manifold (all out of the VK ones), and a MAF seat for a 90mm tube. They are $35 and $25 respectfully. Fitting to the stock manifold is not great since you can only bore it out to ~82mm before you cut into the mounting threads for the TB, but that's still better than the factory 70mm.
Just putting that out there in case anyone was interested in picking up on the development where we left off.

Jared@UpRev.com