The number on the side of the loader is what kubota sets lifting capacity in KG. So your loader 340KG, according to kubota should lift roughly 750lbs at the pins. The weight of the bucket will reduce this number. Also it’s about an 8-10 percent or so reduction capacity at the bucket, or 500mm forward of the pins.
another thing to consider is the front axle load capacity. Your loader will pick up more weight in the first few inches of lift versus max lift height. But without proper ballast, you begin to put not only your loader weight on the front axle, but also the tractor weight. If your lifting your rear tires Off the ground, or are making the rear really light, you will need more ballast not just for safety, but also to even the load across both axles.