I have a 70 loader on my 855, and a 420 loader on my 4310. The 4310 uses those QA brackets that you show. I even have a set in the junk pile that I replaced because the previous owner had strained them. Looked like he lost a pin and then put the bucket in a tiwst. The loader was fine, but the brackets don't tke much lateral stress.
I would have to do some measuring and take some photos, but I think that they would mount on the 70 loader. However, they fit a bucket with a completely different back side profile. I know this because my 70 loader came with a 72" material bucket which was too much for the 855, so I bought a new 60" bucket for it instead. Yesterday I dragged to the old bucket out of the brush so that I could weld the lips and bullet locators on it and use it on the 4310 (the old bucket has a smooth edge and the 4310 bucket has teeth mounted, so it would have been convenient to have both toothed and smooth edges available). The 70 loader bucket has a short backside vertical protion, angling up and away from where those QA mounting bracklets would meet the bucket plate at the top edge. So, I think that they would fit, but the 60/70/70A loader owners would probably render their current buckets non-operational.