Keep in mind that the overwhelming majority of antifreeze / coolant for automotive use is ethylene glycol based. Standard Green (silicate), HOAT, OAT, etc are all predominantly ethylene glycol based with different additive chemistries. A distant second are the propylene glycol coolants, followed by more exotic coolants for racing applications.
Even though Kubota has historically stated in manuals to use "ethylene glycol type" coolant, that doesn't really mean much.
If doing a drain, flush, and fill Kubota small engines can take a wide variety of coolant types. Adding coolant is another matter entirely, and mixing coolant types is almost always a bad idea.
For the OP;
Your machine likely came with Standard Green silicate antifreeze. My last 5 Kubota machines did. I have always switched them out at the first service interval to an HOAT coolant (Zerex G05) for the 5 year maintenance interval, rather than 2 years for the Standard Green. Whatever chemistry you determine to be compatible, 50/50 with distilled water is what to shoot for if you buy concentrated coolant, or straight out of the container for pre diluted coolant.