I grabbed the first image I found on Google and "trimmed" the perfs. (Yes, there are a couple tiny indications of perfs, but I wasn't militant about rotating the stamp to a half degree...I could have left a tiny bit more margin.)

I think they're pretty close in size?
According to Billig, these were printed in sheets of 25. There must have been quite a bit of space between each cliché.
ETA: I don't know why it didn't occur to me to grab an image of a block from the web until after I hit [Enter]...Billig lists dated corner blocks for each color, with 1930, 1931 and 1932 dates for the main entry, and only one mention for the other colors ("dated corner block" with no mention of year).
