I find it implausible that a professional gunsmith and one of the expert witnesses called to testify in the Warren Commission and who spent ten years researching the matter, would not know the difference between an AR 15 and an M-14.
Unless you have proof to the contrary, if the Donahue guy said they had AR 15s, i'm going to believe him.
Photographic evidence. There is a photo of the SS with a M-14 clearly out in the trailing car as it comes out of the triple overpass. At the 6th Floor Museum. Sorry.