I,ve got a new toy. A 1920 mod 99 .303 with 20" barrel with intergal front sight mount with threaded pin. I would like to put on a new Marbles #009840 tang sight. Maybe someone out there with this combo that can give front sight height needed, or measurement from center of aperture on lowest setting to bottom of tang mount. don't want to buy tang sight if I cant find proper sight blade. I know the formula for figuring front sight height but need rear height. Thanks