Nice work, Dave. Based on nearby serial numbers in the Carbine Club newsletters where they review apparent original carbines, I'd say yours is 2178252. Their 2174598 has a 1-44 Underwood barrel, but it also has a low wood stock. 2058xxx has the appropriate high wood stock, but it either has an error in the barrel date or a postwar replacement. The data sheet shows "10-49 Underwood." I would suspect a transcription error, the data sheet is from 1987 - a long time ago when it comes to understanding the carbine production history. This barrel is likely 10-43. Both of these reviewed carbines have S-HB made stocks like yours. So, if you can accept the low wood stock on 2174598 as transitional, replacement, or modified low wood then that leaves us with 2178252.

I don't think SP ever got to 2278252.