I have about 40 pieces of Marathon NOS ad glass. Many different sizes, but the size of the "Marathon" lettering is the same, meaning, if you didn't have the exact ad glass you could take one of the larger ones and cut it down to what you needed.
I believe this was intentionally.
You should list the size you need, but if anyone has some that are larger, they should work, just cut them down.
Author, Gas Pump Identfication books 1st & 2nd Editions & Air Meter Identification books
We rebuild ECO air meters and sell parts.