Well, the drain plugs in my '38 take a 1/2 BSF or 13/16" socket, so maybe that guess is another wrong alley.
How about a change in the wire screen mesh size or height?
They do sell 13/16" wrenches and sockets here, and it is for 9/16" diameter bolts, not very commonly used on new equipment but still around.
In any case you will be fine with a C990/1 in yours.
Or if you want to repair yours as I did, McMaster-Carr sells brass wire cloth in a bunch of mesh sizes. I found I had to tin each piece separately, then use clamps to hold them in position together and solder them.