I wasn't debating your speculations on the gun in question, in fact we seem to agree on it.
However S&W made both the model 27 and 28 in .357, and there were dozens of custom iterations of the M-27 in subsequent years. A lot of Lew Horton specials, Performance Center guns like the 3" 627 V-Comp, and the 627-5 8-shot:
They may all be based on the M-27 but there's certainly more than "one" N-frame .357.
Would you agree though that the top strap is a dead giveaway? I've never seen a Smith with one that thick.