hello again,,well i looked at my refrence books,,and still don't know about the N prefix,,most 1911 comercial models have numbered slides with a C prefix ,,some were made with unumbered slides and the serial number you have could put it in that range but serial number should have the c prefix,,either of the early models listed above are in the 1500-2000 range in the condition you say yours is in,,one of our other moderators refrenced a link to a 1911 colt collectors site that may help out with the N prefix ,,thanks to kim for this link it may be helpful
http://www.sightm1911.com ,,hope it helps with your markings
bigcurt