Great choice! I favor the 6" Smiths. Be sure it's a M19-4 or older P&R (Pinned and Recessed) and the finish is in good shape.
Check-out the topstrap just above the forcing cone for flame-cutting. If there is a witness mark this will indicate the previous owner shot a boat load of the lighter 124 gr speed-balls.
Check the forcing cone for cracks. (especially on the bottom where it's machined for crane clearance.)
Be sure the timing is right and cylinder lock-up is tight.
There is something about a vintage Smith wheel gun in the N or K frame that sends piss-quivers up my spine. Like a vintage M1911A1, the history seems to morph from the ageless stocks and provide the shooter with a glimpse of brilliance from the giants who's shoulders we walk on. (Elmer Keith, Jack Weaver, Col. Charles "Boots" Askins, Thell Reed, Jerry Miculek to name a few.)
Here's mine, a Smith & Wesson model 19-3, P&R. Manufactured in 1970, this gun is older than many members here yet the barrel is clean and shiny and it shoots like......well you decide below;