Peter, yes, I have. I have seen the 408, 509 and 609 mounted on Grand L's. Climbed on them and even operated the controls. Both of the Kubota dealers I talk to here consider them to be the best hoes for the Grand L's.
They have what I would call a four point mount. Two braces are permanently installed over the axles, so there is no subframe attached to the hoe. The braces have slots in them where they protrude from the rear. To mount the hoe you manuever pins on the hoe into the slots. There are two similar mounting points by the upper lift arms. You dont have to remove the lower arms; just fold them out of the way.
The hoes mount very close to the tractor. On one of them the hoe seat was literally on the other side of the ROPS bumping into the tractor seat, which had to be folded forward.
I think there is some sort of spacer that allows you to move the hoe further away. In contrast, Woods hoes seem to protrude way out the back on L's, too far in my view.
The Bradcos have much stronger digging specs than anything else, and are run off the tractor hydraulics. The side to side boom movement is via pistons, not via chain drive like the Kubotas and Woods. And the pistons are mounted up high, away from the dirt. There is also some sort of swing control that dampens the swing movements. They have a website.