I know I'm mostly repeating MrPBody and Molhannah's posts, but I thought I'd chime in anyway.
Both my '67 Impala SS 327 cars came with the Powerglide (although my convert ended up with a TH400 swapped in).
I would say two things are relatively certain;
- There were no TH350's in 1966, so if that's what's in there, its definitely been changed and
- I know of no small block TH400 equipped '66 or '67 Impalas.
I strongly suspect the car came with a 2spd glide and someones swapped in a TH350 or TH400.
Any new info?
Dave