This is special edition (特別収録) from year 1992 containing “Tetsu no Shoujo Jun” (1983) and “UFO Kara Kita Shounen Muu” (1979-1980).
Info (Tetsu no Shoujo Jun): http://www.mangaupdates.com/series.html?id=23377
Info (UFO Kara Kita Shounen Muu): no info, but mentioned in wikipedia article. According to MazingerZ.com, this manga also was included in Nagai Go SF Kessakushuu Vol. 08.