The LA203A seems to be a rare beast! I do have a list of many Kubota loaders, but that particular one isn't on it...quite often I have no idea what equipment customers have when they order so I can't add to the list frequently.
I also hesitate to give measurement advice for fear of being wrong and then having to deal with return and re-shipping fees. I always ask customers to verify because there have been some inconsistency in a few Kubota buckets-for example on the LA240 loader, I've had customers order both the 1-7/16" and the 1-5/8" ones for this loader, why I do not know.
FYI, for those that are curious, the most popular ones are the 1-5/8" hooks, at the least popular are the 2-1/2" ones.