Steve,
Ours were square and were the same size around the aircraft. I don't remember the exact size but on our ships, the white square with red cross went from the cargo door window to the bottom of the cargo door ... and as I said, was square so that would give you the width. Same size was on the nose. We didn't have them anywhere else.
Hope that helps but I'm sure someone will have exact measurements for you. All you'll have to do is convert them to 1/48th scale. By the way, for the 1/48th bird I've done, I've used the decals from the Monogram UH-1 Medevac kit. This is a horrible kit and is a reissue of an old kit but for about $10 it's worth it for the decals and a few spares.
Paul