The original 99 was made from 59-61. The model 99C was made from 62-78, it was grooved for scope mounts. The first 99 was'nt drilled and tapped for a scope. Odds are someone, sometime or another has drilled it for a base. Which is what your going to have to do. If you have a gunshop around that carries a wide variety of bases, your going to have to try a bunch until you find one that will match the radius, and drill and tap the holes. Unless your lucky enough to find the one they used and the holes line up for ya.