Welcome V8z-tek! Your posts can be as long as you want, don't worry about it. The reason you didn't find much on the turbo 400 is one, it's big, and two, it does not have overdrive. Most people here use an overdrive tranny because of the lack of low numerically gears that come stock in the Zs. I don't think you'll want a screaming Z on the highway. If you still want to use the TH400 with JTR mounts, you may have to hammer some of the tunnel, and I'm sure you can modify a turbo 350 mount. I would test fit the combo to see where to hammer.
Good luck!