Interesting information here. I checked mine last night; #4XXX dated 4/69. It is my understanding that the original K-32s were ofered as O/Us. Mine has the same serial number on the receiver and O/U barrels. I also have three top single barrels, all with different serial numbers; dates in the '68 - '69 time frame. I inherited all this from my Dad and I have no idea where the single barrels came from. I know he bought the gun in the O/U configuration, new in 1970. Was the gun also offered as a single barrel ? Thanks.