Ahhhh, gotcha.
There is actually at least one other 6-speed Impala SS. GM has it in what they call their "toy box" where they keep all of their test mules.
It has a lot of company there, or it used to. They used to keep that blue mid-engined Corvette design from the '90s there, but I think that is in Bowling Green right now. Besides that, the '94 Camaro with the big block 510 (called Red Devil) is there, an old Citation X/11 with two engines (one in the rear, one in the front), a couple all wheel drive Berettas, a Caprice with a BMW V-12 engine, an Iroc-Z Camaro with 4 wheel steering, and a bunch of other test mules are either still there, or have been relocated.
Anyway, I read about these cars in an issue of Hot Rod magazine from the summer of 1998. The '94 Impala SS has the T-56 transmission from a Camaro and a custom console to incorporate the stick shift. I may be running myself into a corner... does Tony own this test mule I am writing about? Or was the 6-speed conversion on his done by Callaway?