Very nice!!! Was briefly interested in an M45 but they are very collectible!
With no rebuild marks (that I can see) that might be even more interesting. I thought most of the M1911A1s were rebuilt going into VN.
There are guys on the 1911 boards that know everything and could probably tell you.
Slides below Colt serial 11400001-1145000 should be stamped with the serial under the firing pin plate. Rebuilt guns are seldom numbers matching.