The class of 81' machine came with a 25" monitor not a 24" monitor. 24" color tubes weren't really every a thing, and neither were 28" tubes. (Although perhaps you are in a country which allowed false advertising of tube sizes, which would explain a bit).
Standard color picture tubes went, 13", 19", 25", 27" 30", 33", 36" and 40". Black and white sets had a different array of sizes. As did wide tubes and flat tubes.
The class of 81' machine is also just a more cheaply produced Ms. Pac-Man cabinet. I don't know if the dimensions are 100 percent the same, but if not then they are really close as I have seen them side by side with original Ms. Pac machines at auctions and they looked identical.
I was thinking what to do with my 28" TV and I came to think, how much I like the Class Of 1981 cab. It already has a 24" as a default, so why not make similar cab with a 28" monitor. So anyone got plans for the cab? I checked Jakobuds site and there are plans for similar cabs, but I'd be interested to see the plans for this specific one. Thanks!