I don't know about the Boise, but the Cowell should be able to be the Johnston well enough. That kit is a square bridge Fletcher, as was Johnston. The few images of Johnston on Navsource don't show anything notably unusual to me, and the anti kamikaze fits did not start until July of 1945. Johnston sank in 1944. I think it should be a straightforward build without modification.

Not too long ago, Rick E. Davis read this board, and posted here on US destroyer questions like this. He is a thorough expert on them, having invested hundreds of hours of research. His answers were pure gold. Unfortunately, I haven't seen a post of his here in years. I think all the "turmoil" we generate caused him to stop coming here. A great loss, which I am not able to fill. I know some general things. He knew details.