If the gun is a .38 Special Military and police then it is a Pre Model 10 in common usage. If it is chambered for .38 S&W as you describe then it would be what would become the Model 11. not Model 10. Strictly speaking it isn't a pre anything, Simply a post war Military and Police, regardless of which caliber it is.
Your SN would have shipped approximately 1949, +/- 1 year.