The extractor hook would have to be viewed from below in order to see the extra beveled cut behind the hook. Looks just the same from all other angles.
Back when I bought mine, I was talking to one of the older employees (now retired) and he said he'd never heard of any plans to offer the 4040 with a stainless slide, and it wasn't around long enough to see any variations. Never say never, though ... except ... S&W told you the 4040 had shipped with the standard blued steel slide, right? They only list one slide assembly for the 4040 on the last parts list, too, and no optional versions.
Might the Performance Center have produced a special stainless slide for a 4040 project commissioned by some customer? Never Say Never ... but even if they'd agreed to do so, it might've easily added another $300-$400 dollars to the cost of the gun (not being a standard production slide they could run over and grab from the factory, making it a special production project). Less expensive to just plate the slide and associated parts.
Then, there's the 4040 mag that has the same finish in your pics. If someone had tried to convert a stainless 3913 mag to make that one shiny 4040 mag, it would have the numbers stamped next to the witness holes (which the 4040 mag bodies lack).
The 3913 mags were also folded and welded on the left side, toward the front, while the 4040 mags were welded in the rear, like some other 3rd gen mags (the ground down line can be hard to see, as they did nice grinding and polishing of the mag bodies). BTW, for trivia, I was told by someone at the factory that the "open" part of the weld line at the top of many of their mags was intentional, and the weld wasn't done and closed at the top as a way to reduce stress on the weld, and it actually helped prevent stress cracks.
The 4040 mags were stamped M4040, while the 3913 mags were stamped with a S and a M on the bottom right side ("s" was for stainless, I thought I remembered).
Dunno.
I'd still not be surprised if it turned out to be a case of some version of one of the metal plating processes that may have been used. One with which your friend may not have first hand experience (as done by some particular vendor).
Like I said, very interesting.
If you use this 4040 for a lot of shooting, look to see if any copper flashing might appear at hard wear points, or if some flakes might pop off (depending on whether it's plated, and the amount of prep work that may have been involved).
I've got an early 70's Commander I had electroless nickel plated in the 80's, with a subdued satin finish. It took some time, but eventually signs of some small flakes coming off began to appear in some hard wear spots. Kinda of looks like brushed stainless to the casual eye.
Still a nice find, though. If it were mine, I'd shoot the dickens out of it and enjoy it.
).
Just some thoughts out of idle curiosity.
