The 6-inch barrel was introduced in late 1963 and would have been after the 19-2 model variation was introduced. The barrel is not original to the revolver you are looking at.
Thanks.
I just got to see the revolver in hand, and no mystery. Although registered (Canada Eh!) as a Model 19 no dash it is in fact a Model 19-3.
In great condition with very faint drag line so had to buy it anyway, and price seemed "right".
Cheers