Yep, that's the TB from the Mustang. The original casting was horrible. You can see in the first pic that the leading edge had a huge lip on it. I tapered that down. There was also a nasty ridge inside, which I completely cut down too.

As to the butterfly - I removed half of the shaft myself. You can't see in in the second pic, but I basically cut off the top half of the shaft. The bottom half is left, and is threaded, so the screws can bite into it. I'm going to countersink the screws so that the heads don't stick up and cause any obstruction either. I completely polished and knife-edged the butterfly too. Overall there's a good 10-20% more cross flow area than there was before. (Edit: You can even grind down a significant amount of material off the bottom shaft too, if you really want to go radical. The shaft doesn't need to be anywhere as thick as it is, you can easily grind down a couple millimeters. Just make sure you leave some meat around the screw holes.)

I've heard ZOOP is good, never actually tried it though. I'm still partial to the Al Oxide paste. Lots of companies make it, you can pick it up just about anywhere.