bucket weight is around 800 as is. They have bolt on grapples, but honestly, you'd be better of with a QA one, you've got a built in QA. Check out Markham.
I do love my 4n1, but its not a grapple - they do different things, I wouldn't say picking up is its strong point. But it does clamp in a different way then the grapple does, I find both useful.
I actually came on to put out some info on the backhoe quick coupler. I've found the lynch pin that holds the quick couple pin on comes off very easily. I just got a replacement, (both pins) and in a few hours of digging lost the lynch pin again despite wiring it on. With 2 separate wires no less. Granted this is digging stumps, so its easy for things to catch.
But no more lynch pin for me on the backhoe bucket. I'm going out to buy a grade 5 bolt and will put it on with my portable impact driver. Honestly, that's probably going to be as fast to change as the regular lynch pin was - despite coming off easily while working, it was a pain for me to remove. And I don't change backhoe buckets that often.