This from Wix re; their 51438 and a replacement Wix for late model GRiSO;
"51348 is a 21 micron filter.
57035 is shorter at 32 micron , used on Briggs and Stratton engines and Kawasaki Small engines.
Just an FYI, you said you think you understand why I can’t recommend a replacement WIX filter.
The truth is , because we don’t have anything that will meet their specifications and that is what you’re seeing now.
I would not recommend a WIX filter for this application because we do not offer a suitable replacement."