This is what I have been doing, but it is slow and I need the attachment as close to the bottom of the bucket as I can get. I don't like the hook, eye or whatever attached to the top of the bucket as visibility is much better on the bottom and I can get real close visually and mechanically to the item to be lifted.
Pictures of what you’re trying to accomplish would probably help. May be missing the crux of the problem your solving but on the chance I do understand…
I’m thinking if I wanted a eye type attachment point just below the leading edge of the bucket:
1) I’d want it to be something that didn’t put a heavy point load on the bucket lip because smiles are not good things on loader buckets. If an eye bolt in the center, I’d be putting a spreader plate on as a washer with the bolt.
2) I’d want it to be quick on/off so I could still use the bucket as a bucket and not need two wrenches, 10 minutes, and a place on a shelf to store the stuff every time I swapped it.
3) Lifting 400lb ain’t pushing the loader but if it fell that would suck and if it landed on me or someone else, that’s just unacceptable, so I’d want a solid positive connection with substantial safety factor.
That’s leading my mind to a setup like Bmyers above with a chain between the two grab hooks such that the slack in between would hang down below the bucket edge a little (or a lot if you prefer) and use a clevis hooked to the chain for the lifting eye. If the chain was trying to fall back in the bucket when no weight on, roll the bucket forward until it doesn’t fall back in the bucket. Once the weight is on it, roll the bucket back a little and if it isn’t much chain below the bucket it isn’t going to twist or have much swing.
As I said above I have not done that type setup with the Kubota because I have other options I prefer with it. Pre-Kubota lifting with the trip bucket loader on the Farmall H (which is an antique curiosity but will lift around 1600lb +/-) that was one of two common ways to attach loads. Other way was run a single line of chain over the bucket edge, which is quick and easy but allows much more swing and twist of load. The loop method with clevis to attach the load provides good stability for the load.
Maybe with what you’re doing you need the slightly more solid eye bolt but don’t see how you can do that without installing the eye bolt (and spreader plate if you use one) to lift, and removing to use as a bucket every time you change jobs, which seems like a PITA but may be acceptable if you aren’t changing often.
If I’m missing the point of what you’re trying to accomplish just ignore all that.
Edit: Just noticed in rereading your original post you already did the eyebolt thing. Hope that works well for you.