Probably 1955 or '56 with that S/N. Pre-model marked kit guns are sort of in demand these days, so I've got to believe the price on one like you describe is at least $700-800. Maybe even higher. I follow the prewar Kit Guns pretty closely, but the postwar, pre-model-marked KGs are not as familiar to me.
You didn't say, but is this by an chance an airweight version? And does it have fixed or target sights?
A model of 1953 Kit Gun would be a pre-Model 34. The airweight version would be a pre-model 43. I think most 2-inch barrels came with fixed sights, but some are known with adjustable rear sights. The Standard Catalog says they were used as training guns.
Sounds like a nice piece. Can you show some photos? There's a photo how-to thread in the Forum Office section of these boards.
Welcome to the forum. Nice to have another Californian here.