These are a pretty neat little item. The '64 Topps Stand-ups are not an 'insert' but a 'stand alone' product (no pun intended). They came in one cent and five cent packs or so I've read. I have no recollection of ever seeing them for sale but I have vague memories of seeing them back in the day.
I picked up the four Orioles from the 77 card set at shows or through the mail back in the 80s when I was buying anything and everything that said 'Orioles'. Looking quickly online I can see that these are far more costly than the other 'secondary' Topps products I've been chasing. I wouldn't mind having a couple of the others off the checklist, Johnny Callison and Rocky Colavito for starters, but it is no priority.
Of the 77 cards 22 were single printed and more scarce. None of the Orioles are in that category.
Yes, my Norm Siebern has colors that appear 'off' when compared with the others. I don't know if that is a result of the printing or age. He had just come over from Kansas City prior to the '64 season and so he is airbrushed into orioles gear sort of haphazardly.
The backs of these are blank cardboard, like cards cut from cereal boxes. Brooks Robinson's card is by far my favorite of the group. It's got the best picture, best pose and well, it's Brooks!!!