1/2 shafting is good. I did that on my 3.0.
TB spacers were good for downdraft carbeurators and TBI systems. They gave the fuel/air a chance to mix and bend around the turn into the manifold eeasier.
The problem is that sidedraft, long plenum systems like ours really don't need them. There's a ton of space already behind the TB, and in addition, our port injected engines don't even mix air/fuel until right over the valve -- meaning a little length at the TB isn't going to do ANYTHING.
So, the spacers did have their place at one time -- but modern engine configurations don't benefit from them.