The Woods BH750 doesn't have one. But on some of the other Kubota backhoes that mount to the 3ph, there is a limiter bar that snugs up underneath the 3ph lower arms, about 1/2 way along their length, locking the backhoe in a little more securely. (If material strength was infinite, the mast ear could be removed from the top link bracket and the weight of the backhoe carried entirely by the lower arms, but I don't plan to test that theory! )
It also swings down and makes a handy stand when the backhoe is removed from the tractor.
Something similar could be fabricated for your L4620, I'm sure. I'll take some pictures of mine but at the moment mine is off the tractor as I'm using the landplane to touch up my driveway. So it will be a few days.