Andre got ones of these right?
Those monitors were in two version.
One was an A51 semi-flat tube and this one that is more difficult to find, that is an A48 curved tube.
This is a direct replacement in Sega cab for example.
I also use one of them in a Time Scanner cab, in a Powerdrift upright cab, and my friend in his Super Hang On upright.
The A51 instead is not a direct replacement, but if you have space inside the cabinet is not a problem.
Since i also own some of the A51 version, i manage to fit them in some 20" jamma generic cabs.
Both are great looking monitors (as they are new), but for sure the curved A48 models are way better for old 20" dedicated cabs.