And you only get two scans.
4985023: At first I believed this was from the 1972 Kankan Menko set (JCM 15a), however, the front image points to it being from the 1973 Thick Menko set (JCM 15b). That said, the description for set doesn't recognize this back (two cartoon characters opposing each other). Therefore, I believe it to be a third type, with the cartoon character backs. The player on the front is Shigeo Nagashima, one of the key cards in the set. (Based on the descriptions of Nagashima's cards in 15a and 15b, I believe it to be the 15b card. However, it could be the "headshot" or even "batting" pose for Nagashima in the 15a set. See how difficult this is?)
1750740: This card has the same back style as the Nagashima card, but the front is definitely a colorized image that matches up with the JCM 15a set. Therefore, this is a JCM 15a card of Minoru Murayama, with Toshio Kanbe in the background.
80620: This card is definitely from the 1973 Thick Menko set, and features Toshimitsu Suetsugu. The back is identical to the JCM 15a Type I style, making this a Type I back for JCM 15b.
90001: Marusan issued a bunch of very similar cards around 1960-1964 or so, but given the information on the front, this is from JCM 11, 1964 Marusan Simple, Navy Blue Back Photo Menko. Cards from this set were imported to the US, and those cards have a stamp around the janken symbol with a card number. This particular card stayed here in Japan. The player on the front is Kent Hadley, and this is one of only two menko sets (and thus Japanese sets) he appeared in!
The blue-backed one: Not really a menko card despite its appearance, this thinner stock card was issued by NST as a parallel to JMC 40: 1978 NST Yomiuri Giants. The regular cards in this set were meant to be pasted in an album, but these cards might have been sold as sets or given away as premiums/bonuses. I'm not sure who the player is.
I'm finally finished! But there are more menko to come. I have an uncut sheet and some other menko surprises on the way. But those are baseball menko. I promise!