Well, it's more of a B-36 derivative idea, but there apparently was a study done of converting the X-3 for air launch from a XB-60 (apparently gave better clearance than being carried under a B-52 wing). I could see a NACA/NASA-marked B-60 carrying a manned X-3 or a USAF one carrying an AGM derived from the X-3, but, say, with better engines.