You have a KS98 (Extra-Seitengewehr). Commonly called a dress or walking out bayonet. It appears to be the long version. Made by E.& F. Horster & Co. It is double maker marked, which is less common than the single maker marked examples. It was also used by the R.F.V. (Reichsfinanzverwaltung) the stamp on the cross guard denotes that, another plus. There is an excellent post by forum member Stephan98k about the R.F.V. It is in the Mauser Rifles 1933 to 1945-The Nazi Period sub forum. Posted on 10-17-19. Can not tell for sure from pics but, blade appears to not be sharpened and is in fair shape with some finish loss or corrosion. The cross guard and pommel have lost most if not all of the finish. What I can see of the grips looks good,no cracks or damage. Do you have the scabbard? Not a bad KS98 due to the extra stamps. Better even since it was brought back by your dad.