I'll have to research that again. I thought I found information that they made one in 84mm, but this photo may not actually be one.
It could well be 84mm - I've seen weirder stuff. One reason to suspect 84mm is the lack of key ring - all of the Spartans in this model had the keyring. The fact that this one does not is enough to raise the question.
Below is the "official" flyer for the 1991 anniversary models. Note that is doesn't include to 100th anniversary Climber either, so obviously it's not complete. Also of note is that for the 1991 anniversary, the Climber (Traveler actually) that I just mentioned is the only one with a serial number. This is in contrast to the 1984 anniversary where the Champion, Tourist and Tinker Small all had numbers and the 1997 anniversary where both the Spartan and Swiss Champ had numbers.