The SN isn't right for a Colt 1917 Army model. and the barrel is too short. The WW1 military revolvers had wooden grips. The revolver you're looking at looks like a civilian model, but I don't know if civilian models post WW1 were produced in .45 ACP. I think it's worth some study before investing money in it.

As said, the Army models were marked as such. If it is, it's almost certainly to have been cut down.