Which X1 Box used for Older TV - Non HDTV

Parents have a Toshiba 2004 CRT TV which still works fine. Very heavy but pitcure looks good. So its not HDTV only 4:3 SD Screen Square. So comcast hooked up a small Maybe a PACE XID P2 HD Box to  the tv so the Lowest resolution in the X1 settings is 720P which doesn't make sense this like I said this not an HDTV. So the picture on SD channels doesn't fit the screen and when I do use the HD channels they look weird also with 720P resolution. Basically which X1 supports older tv's like No HD?