Actually the underwing aerial was on several earlier versions which also had the aerial mast as well i believe they were for two separate radio sets. I 've included a picture of a G-10 to illustrate. I only have one actual photograph of a K-4 with a radio mast and it does'nt show the side with the underwing aerial.although I do have several profiles which show the antenna mast on k-4s so that's not an issue anymore what we need to know is whether the k-4 had both sets fitted like earlier models.