The 1961 stamps were an insert to the regular wax packs. I can't say with 100% certainty, but I'm pretty sure that they were the first inserts into Topps packs. They were issued in two-stamp panels, 208 different stamps thought 207 players; Al Kaline has two different stamps.
The stamps were shaded in brown or green, divided equally with 104 of each color. The stamps weren't numbered, so most catalogs list them in alphabetical order. A 10¢ album was also sold and the stamps were to be placed in the albums.
The Cubs managed to land twelve players on the checklist. With 18 MLB teams that season, twelve is spot on to evenly spread the teams. The twelve Cubs are also split evenly between brown and green.
The 1961 Cubs were not very good: a 60-94 record was good for a seventh out of eight teams finish. They did have four future hall of famers, and each had a stamp.
When you look over the rest of the stamps, you'll understand why the team wasn't very good.
I'll wrap up with a tile of all twelve, looking kinda like a sheet of stamps you'd buy at the post office. In 1961 that sheet of twelve stamps would have cost you 48¢. Today you're paying $5.88.