Pre what war? Viet Nam, maybe, the Model 19 came out in 1955.
And sure enough, yours is a first year gun. It does not have a model number stamp because model numbers were not assigned until 1957. Yours is a Combat Magnum and that is that. Some collectors would call it a "pre 19" because it is no different from a model numbered revolver.
The Y number is an "assembly number" used for factory tracking and disregarded after the gun is serial numbered and shipped.
Do you have the original walnut grips? The Hogue is aftermarket.